IIT JEE 2010 Solution
Transcription
IIT JEE 2010 Solution
® SOLUTIONS TO IIT-JEE 2010 Paper-I (Code: 8) Please read the instructions carefully. You are allotted 5 minutes specifically for this purpose. INSTRUCTIONS A. General: 1. This Question Paper contains 28 pages having 84 questions. The question paper CODE is printed on the right hand top corner of this sheet and also on the back page of this booklet. 2. No additional sheets will be provided for rough work. 3. Blank papers, clipboards, log tables, slide rules, calculators, cellular phones, pagers and electronic gadgets in any form are not allowed. 4. The answer sheet, a machine-gradable Objective Response Sheet (ORS), is provided separately. 5. Write your Registration No., Name and Name of centre and sign with pen in appropriate boxes. Do not write these anywhere else. B. Question paper format and Marking scheme: 6. The question paper consists of 3 parts (Chemistry, Mathematics and Physics). Each part consists of four Sections. 7. For each question in Section I, you will be awarded 3 marks if you have darkened only the bubble corresponding to the correct answer and zero mark if no bubbles are darkened. In all other cases, minus one (–1) mark will be awarded. 8. For each question in Section II, you will be awarded 3 marks if you darken only the bubble(s) corresponding to the correct answer and zero mark if no bubbles are darkened. Partial marks will be awarded for partially correct answers. No negative marks will be awarded in this Section. 9. For each question in Section III, you will be awarded 3 marks if you darken only the bubble corresponding to the correct answer and zero mark if no bubbles are darkened. In all other cases, minus one (–1) mark will be awarded. 10. For each question in Section IV, you will be awarded 3 marks if you darken the bubble corresponding to the correct answer and zero mark if no bubble is darkened. No negative marks will be awarded in this Section. ® IITJEE 2010 SOLUTIONS 2 SOLUTIONS TO IIT-JEE 2010 CHEMISTRY: Paper-I (Code: 8) PART – I Useful Data Atomic numbers: Be = 4; C = 6; N = 7; O = 8; Al = 13; Si = 14; Cr = 24; Fe = 26; Zn = 30; Br = 35. 1 amu = 1.66 × 10–27 kg R = 0.082 L atm K–1 mol–1 –34 h = 6.626 × 10 Js NA = 6.022 × 1023 me = 9.1 × 10–31 kg e = 1.6 × 10–19 C 8 –1 c = 3.0 × 10 m s F = 96500 C mol–1 RH = 2.18 × 10–18 J 4o = 1.11 × 10–10 J–1 C2 m–1 SECTION – I Single Correct Choice Type This section contains 8 multiple choice questions. Each question has four choices (A), (B), (C) and (D), out of which ONLY ONE is correct. Note: Questions with (*) mark are from syllabus of class XI. 1. Plots showing the variation of the rate constant (k) with temperature (T) are given below. The plot that follows Arrhenius equation is (B) k (A) k (C) k T T (D) T Sol.: As per Arrhenius equation (k AeEa / RT ), the rate constant increases exponentially with temperature. Correct choice: (A) 2. In the reaction HBr OCH3 (A) Br Br and CH3OH H+ OCH3 Sol.: T the products are OCH3 and H2 (C) k + Br– O–CH3 (B) Br and CH3Br (D) OH and CH3Br OH + CH3Br H Correct choice: (D) 3. The correct statement about the following disaccharide is CH2OH H HOH2C O H (a) OH H H OCH2CH2O HO H Sol.: OH H O H (b) HO CH2OH OH H (A) Ring (a) is pyranose with -glycosidic link. (C) Ring (b) is furanose with -glycosidic link. Correct choice: (A) (B) Ring (a) is furanose with -glycosidic link. (D) Ring (b) is pyranose with -glycosidic link. *4. The synthesis of 3-octyne is achieved by adding a bromoalkane into a mixture of sodium amide and an alkyne. The bromoalkane and alkyne respectively are (A) BrCH2CH2CH2CH2CH3 and CH3CH2CCH (B) BrCH2CH2CH3 and CH3CH2CH2CCH (C) BrCH2CH2CH2CH2CH3 and CH3CCH (D) BrCH2CH2CH2CH3 and CH3CH2CCH Sol.: CH3CH2CCH NaNH2 –NH3 CH3CH2CC– Na+ CH3CH2CH2CH2Br (SN2) CH3CH2CCCH2CH2CH2CH3 + NaBr 3-Octyne Correct choice: (D) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 5. Sol.: 6. 3 The ionization isomer of [Cr(H2O)4Cl(NO2)]Cl is (A) [Cr(H2O)4(O2N)]Cl2 (B) [Cr(H2O)4Cl2](NO2) (C) [Cr(H2O)4Cl(ONO)]Cl (D) [Cr(H2O)4Cl2(NO2)].H2O Ionization isomer of [Cr(H2O)4Cl(NO2)]Cl is [Cr(H2O)4Cl2]NO2. Correct choice: (B) The correct structure of ethylenediaminetetraacetic acid (EDTA) is CH2–COOH COOH HOOC–H2C HOOC N–CH2–CH2–N N–CH=CH–N (A) (B) HOOC HOOC–H2C COOH CH2–COOH (C) HOOC–H2C COOH CH2 H HOOC–H2C N–CH–CH–N (D) H CH2–COOH CH2 CH2–COOH N–CH2–CH2–N CH2–COOH HOOC–H2C HOOC Sol.: The correct structure of EDTA is HOOC–H2C N–CH2–CH2–N HOOC–H2C CH2–COOH CH2–COOH Correct choice: (C) *7. Sol.: *8. Sol.: The bond energy (in kcal mol–1) of a C–C single bond is approximately (A) 1 (B) 10 (C) 100 (D) 1000 348 C–C bond energy = 348 kJ/mol kcal/mol = 82.85 kcal/mol 100 kcal/mol. 4 .2 Correct choice: (C) The species which by definition has ZERO standard molar enthalpy of formation at 298 K is (A) Br2 (g) (B) Cl2 (g) (C) H2O (g) The species in its elemental form has zero standard molar enthalpy of formation at 298 K. (D) CH4 (g) Br2(l) Br2(g) ; H of 0 C(s) + 2H2(g) CH4(g) ; H of 0 H2(g) + ½O2(g) H2O(g) ; H of 0 Correct choice: (B) SECTION – II Multiple Correct Choice Type This section contains 5 multiple choice questions. Each question has four choices (A), (B), (C) and (D) out of which ONE OR MORE is/are correct. 9. In the reaction OH NaOH(aq)/Br2 the intermediate(s) is(are) O O O O Br (A) (B) OH O NaOH (I) O Br Br2 –Br– –H2O Br O O (D) Br Br Br Br Sol.: (C) Br Br2 Br2 –Br– –Br– Br Br Br Br (II) (III) (IV) Product of reaction of phenol with NaOH/Br2 is sodium salt of 2,4,6-tribromophenol. Hence, species (I), (II), (III) are formed as intermediate. Correct choice: (A), (C) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS *10. Sol.: *11. Sol.: 4 Among the following, the intensive property is (properties are) (A) molar conductivity (B) electromotive force (C) resistance (D) heat capacity Mass independent properties are intensive properties. Resistance and heat capacity are extensive properties. Correct choice: (A), (B) The reagent(s) used for softening the temporary hardness of water is(are) (A) Ca3(PO4)2 (B) Ca(OH)2 (C) Na2CO3 (D) NaOCl Temporary hardness is due to bicarbonates of calcium and magnesium. Temporary hardness can be removed by Clark’s process, which involves the addition of slaked lime, Ca(OH)2. Washing soda (Na2CO3) removes both the temporary and permanent hardness by converting soluble calcium and magnesium compounds into insoluble carbonates. Ca(HCO3)2 + Ca(OH)2 2CaCO3 + 2H2O Ca(HCO3)2 + Na2CO3 CaCO3 + 2NaHCO3 2OCl– + 2H2O 2HOCl + 2OH– Ca(HCO3)2 + 2OH– CaCO3 + CO 32 + 2H2O Correct choice: (B), (C), (D) *12. Sol.: Aqueous solutions of HNO3, KOH, CH3COOH and CH3COONa of identical concentrations are provided. The pair(s) of solutions which form a buffer upon mixing is(are) (A) HNO3 and CH3COOH (B) KOH and CH3COONa (C) HNO3 and CH3COONa (D) CH3COOH and CH3COONa Any solution of a weak acid and its salt with strong base acts as an acidic buffer solution. If volume of HNO3 solution added is less as compared to that of CH3COONa solution, it results in the formation of an acidic buffer solution. CH3COONa + HNO3 CH3COOH + NaNO3 Excess limiting reagent MV MV – – M(V – V) 0 MV MV (V < V) Correct choice: (C), (D) *13. In the Newman projection for 2,2-dimethylbutane X CH3 H3C H H Sol.: Y X and Y can respectively be (A) H and H (B) H and C2H5 Structural formula of 2, 2-dimethylbutane is CH3 1 2 3 (C) C2H5 and H (D) CH3 and CH3 4 CH3–C–CH2–CH3 CH3 (I) Newman projection using C1–C2 bond H 2 H3 C CH3 1 H H C2H5 (II) Newman projection using C3–C2 bond CH3 2 CH3 CH3 3 H H CH3 Correct choice: (B), (D) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 5 SECTION III Paragraph Type This section contains 2 paragraphs. Based upon the first paragraph 3 multiple choice questions and based upon the second paragraph 2 multiple choice questions have to be answered. Each of these questions has four choices A), B), C) and D) out of which ONLY ONE is correct. Paragraph for Question 14 to 16 Copper is the most noble of the first row transition metals and occurs in small deposits in several countries. Ores of copper include chalcanthite (CuSO4.5H2O), atacamite (Cu2Cl(OH)3), cuprite (Cu2O), copper glance (Cu2S) and malachite (Cu2(OH)2CO3). However, 80% of the world copper production comes from the ore chalcopyrite (CuFeS2). The extraction of copper from chalcopyrite involves partial roasting, removal of iron and self-reduction. 14. Partial roasting of chalcopyrite produces (A) Cu2S and FeO (B) Cu2O and FeO (C) CuS and Fe2O3 Sol.: 2CuFeS2 + 4O2 Cu2S + 3SO2 + 2FeO Partial roasting of FeS and Cu2S produces FeO and Cu2O respectively. 2FeS + 3O2 2FeO + 2SO2 2Cu2S + 3O2 2Cu2O + 2SO2 Correct choice: (B) 15. Iron is removed from chalcopyrite as (A) FeO (B) FeS FeO + SiO2 FeSiO3 Correct choice: (D) Sol.: 16. Sol.: (D) Cu2O and Fe2O3 14001450 ºC In self-reduction, the reducing species is (A) S (B) O2– (C) Fe2O3 (D) FeSiO3 (C) S2– (D) SO2 Cu2S + 2Cu2O 6Cu + SO2 The reducing species is the one which gets oxidized. So, it is S2– ion getting oxidized to S4+. Correct choice: (C) Paragraph for Question 17 to 18 The concentration of potassium ions inside a biological cell is atleast twenty times higher than the outside. The resulting potential difference across the cell is important in several processes such as transmission of nerve impulses and maintaining the ion balance. A simple model for such a concentration cell involving a metal M is M(s) | M+(aq; 0.05 molar) || M+(aq; 1 molar) | M(s) For the above electrolytic cell the magnitude of the cell potential |E cell| = 70 mV. 17. Sol.: For the above cell (A) Ecell < 0; G 0 (B) E cell 0; G 0 (C) E cell 0; Gº 0 (D) E cell 0; Gº 0 (A): M(s) M A (aq) e (C): M C (aq) e M(s) MC (aq) MA (aq) E cell E ocell RT [M A ] RT [M C ] ln ln F F [M C ] [M A ] Ecell = 0.059 log (E ocell 0) [M C ] 0.05 0.07V = 0.059 log (M C ) = 0.059 log 20 [M C ] = 0.059 (log 20 + log [M C ] ) 0.05 Since [M C ] is greater than 0.05 M, so Ecell is +ve. Ecell > 0 & G 0. Correct choice: (B) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 6 If the 0.05 molar solution of M+ is replaced by a 0.0025 molar M+ solution, then the magnitude of the cell potential would be (A) 35 mV (B) 70 mV (C) 140 mV (D) 700 mV [M C ] 2 Sol.: Ecell = 0.059 log = 0.059 log 400 [M C ] = 0.059 log (20) [M C ] = 0.059(2 log 20 + log [M C ] ) 0.0025 0.07 = 0.059 2 = 0.14 V = 140 mV. 0.59 Correct choice: (C) SECTIONIV Integer Answer Type This section contains TEN questions. The answer to each questions is a single digit integer ranging from 0 to 9. The correct digit below the question number in the ORS is to be bubbled. 18. 19. In the scheme given below, the total number of intramolecular aldol condensation products formed from ‘Y’ is 1. O3 2. Zn, H2O Y 1. NaOH(aq) 2. heat OH O 1. O3 2. Zn, H2O Sol.: NaOH(aq) heat –H2O O O O (Y) The number of intramolecular aldol condensation products (, -unsaturated carbonyl compound) formed from (Y) is 1. The answer is 1. 20. Amongst the following, the total number of compounds soluble in aqueous NaOH is H3C CH3 N COOH OCH2CH3 OH CH2OH OH NO2 Sol.: *21. Sol.: CH2CH3 CH2CH3 COOH H3C N CH3 All carboxylic acids and phenols are soluble in aqueous NaOH. Four compounds are soluble in aqueous NaOH. The answer is 4. Amongst the following, the total number of compounds whose aqueous solution turns red litmus paper blue is KCN K2SO4 (NH4)2C2O4 NaCl Zn(NO3)2 FeCl3 K2CO3 NH4NO3 LiCN KCN, K2CO3 and LiCN are the salts of weak acid and strong base. So, their aqueous solutions turns red litmus paper blue. (NH4)2C2O4 is a salt of weak base (NH4OH ; Kb = 1.8 × 10–5) and weak acid (HOOC.COOH ; K a1 = 5.4 × 10–2 and K a 2 = 5.2 × 10–5 ). As a result, the extent of hydrolysis of NH 4 will be more than that of C 2 O 24 and hence the resulting solution will be acidic. The answer is 3. *22. Based on VSEPR theory, the number of 90 degree F–Br–F angles in BrF5 is Sol.: According to VSEPR theory, number of electron pairs around central atom (Br) are 6. N 75 = = 6. (Five are bond pairs and one is lone pair ) 2 2 Its geometry is octahedral but due to lone pair–bond pair repulsion, the four fluorine atoms at corner are forced towards the upper fluorine atom thus reducing F–Br–F angle from 90° to 84.8°. F F F Br F .. F The answer is 0. Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 7 *23. Sol.: The value of n in the molecular formula BenAl2Si6O18 is It is the formula of Beryl (which has BeO, Al2O3 and SiO2). The formula of Beryl should be 3BeO. Al2O3.6SiO2 Or Total cationic charge = Total anionic charge 2n + 6 + 24 = 36 n=3 The answer is 3. *24. A student performs a titration with different burettes and finds titre values of 25.2 mL, 25.25 mL, and 25.0 mL. The number of significant figures in the average titre value is The least significant figure in titre values is 3. 25.2 25.25 25 75.4 Average titre value = 25.1 3 3 The number of significant figures in average titre value will also be 3. The answer is 3. Sol.: 25. Sol.: 26. Sol.: The concentration of R in the reaction R P was measured as a function of time and the following data is obtained: [R] (molar) 1.0 0.75 t(min.) 0.0 0.05 The order of reaction is The integrated form of a zero-order reaction is [A0] – [At] = k0t 1.0 – 0.75 = k0 × 0.05, k0 = 5 1.0 – 0.4 = k0 × 0.12, k0 = 5 The answer is 0. 235 92 U The number of neutrons emitted when 92 U 235 0 n 54 Xe 1 142 38Sr 90 0.40 0.12 0.10 0.18 undergoes controlled nuclear fission to 142 54 Xe and 90 38 Sr is y 0n 1 235 + 1 = 142 + 90 + y y = 4. The number of neutrons emitted are (4 – 1) = 3. The answer is 3. *27. The total number of basic groups in the following form of lysine is H3N–CH2– CH2–CH2–CH2 O CH—C O H2N Sol.: The basic groups in the given form of lysine is NH2 and CO 2 . The answer is 2. *28. The total number of cyclic isomers possible for a hydrocarbon with the molecular formula C4H6 is Sol.: The number of cyclic isomers for a hydrocarbon with molecular formula C 4H6 is 5. The structures are CH3 , , , CH3 and CH2 . Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 8 SOLUTIONS TO IIT-JEE 2010 MATHEMATICS: Paper-I (Code: 8) PART – II SECTION – I Single Correct Choice Type This section contains 8 multiple choice questions. Each question has four choices (A), (B), (C) and (D) for its answer, out of which ONLY ONE is correct. 29. The value of lim x0 1 x 3 x 0 t ln(1 t ) t4 4 (A) 0 dt is (B) x Sol.: lim 1 x0 x 3 x 0 t ln1 t 4 t 4 dt lim x4 4 x 0 3x 2 lim t ln1 t 0 t4 4 x0 x ln1 x lim x ln1 x 1 12 x 0 3x x 4 4 (C) 1 24 (D) 1 64 dt 3 0 form Applying L. Hospital Rule 0 ln1 x 1 1 1 lim lim 4 3 x0 x 12 x0 x 4 Correct choice: (B) 30. x 1 The number of 3 3 matrices A whose entries are either 0 or 1 and for which the system A y 0 has exactly two distinct z 0 solutions, is (B) 29 1 (A) 0 Sol.: (C) 168 (D) 2 For any matrices A it form three planes. But three planes can not intersect exactly at two distinct points. Correct choice: (A) 31. Let P, Q, R and S be the points on the plane with position vectors 2iˆ ˆj, 4iˆ, 3iˆ 3 ˆj and 3iˆ 2 ˆj respectively. The quadrilateral PQRS must be a (A) parallelogram, which is neither a rhombus nor a rectangle (B) square (C) rectangle, but not a square (D) rhombus, but not a square Sol.: If O is origin OP 2iˆ ˆj; OQ 4iˆ ; OR 3iˆ 3 ˆj; OS 3iˆ 2 ˆj QS OS OQ 7iˆ 2 ˆj PR 5iˆ 4 ˆj QS 49 4 53 ; PR 25 16 41 PQ 6iˆ ˆj 37 ; QR iˆ 3 ˆj 10 RS 6iˆ ˆj 37 ; SP iˆ 3 ˆj 10 Opposite sides are parallel and equal but diagonals are not equal. Correct choice: (A) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 32. 9 Let be a complex cube root of unity with 1 . A fair die is thrown three times. If r1 , r2 and r3 are the numbers obtained on the die, then the probability that r1 r2 r3 = 0 is (A) Sol.: 1 18 1 9 (B) (C) 2 9 (D) 1 36 nS 6 3 216 E is the event that r1 r2 r3 0 , is possible if one among r1 , r2 , r3 is of the form 3n ; another one is of the form 3n 1 and the remaining one is of the form 3n 2 , where n Z . For 3n , two possible cases are 3, 6 For 3n 1 , two possible cases are 1, 4 For 3n 2 , two possible cases are 2, 5 nE 2 2 2 3 ! 48 PE nE 48 2 nS 216 9 Correct choice: (C) 33. Equation of the plane containing the straight line x y z and perpendicular to the plane containing the straight lines 2 3 4 x y z x y z and is 3 4 2 4 2 3 Sol.: (A) x 2 y 2 z 0 (B) 3x 2 y 2 z 0 Plane P2 contains the line L x y z 2 3 4 (C) x 2 y z 0 (D) 5x 2 y 4 z 0 Plane P1 contains the lines L1 and L 2 , where L1 x y z x y z and L2 3 4 2 4 2 3 Let direction ratio of normal to the plane P1 is , , , then 3 4 2 0 and 4 2 3 0 8 1 10 Let direction ratio of normal of required plane is (a, b, c), then 8a b 10c 0 ; 2a 3b 4c 0 a b c a b c 26 52 26 1 2 1 Required plane is x 2 y z 0 Correct choice: (C) Alternative: n a b c a .c b a .b c 26 3iˆ 4 ˆj 2kˆ 26 4iˆ 2 ˆj 3kˆ 26iˆ 52 ˆj 26kˆ direction ratio of normal of required plane is 1, 2, 1 Equation is x 2 y z 0 *34. If the angles A, B and C of a triangle are in an arithmetic progression and if a, b and c denote the lengths of the sides opposite to A, B and C respectively, then the value of the expression (A) 1 2 (B) 3 2 a c sin 2C sin 2 A is c a (C) 1 (D) 3 Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS Sol.: 10 Since A, B, C are in A.P. 2B A C A B C 180 3B 180 B 60 a c sin 2C sin 2 A c a sin A sin C .2 sin C cos C 2 sin A cos A 2cos C sin A sin C cos A 2 sinA C 2 sin 2B 2 sin120 sin C sin A 2 3 3 2 Correct choice: (D) 35. Let f, g and h be real-valued functions defined on the interval [0, 1] by f ( x) e x e x , g ( x) xe x e x 2 2 x2 h( x) x e e x2 f x e x e x 2 2 g x xe x e x 2 2 hx x 2 e x e x 2 2 2 and . If a, b and c denote, respectively, the absolute maximum of f, g and h on [0, 1], then (A) a b and c b Sol.: 2 (B) a c and a b 2 2 f x 2 x e x e x 2 2 2 g x 2 x xe x e x e x 2 (C) a b and c b (D) a b c 2 2 2 h x 2 x 3 e x 2 x e x e x for x [0, 1] f x , g x and h x 0 1 1 1 f x , g x and hx will be increasing functions and their maximum values are a e , b e , c e e e e at x 1 abc Correct choice: (D) Alternative: f x e x 1 2 e x2 2 as x [0, 1] e x [1, e] 1 1 f t t , t [1, e] ; max f t e e t max f x e 1 e hx g x f x g x e 1 1 1 but at x 1 , g x e and similarly at x 1 , hx e e e e So, a b c *36. Let p and q be real numbers such that p 0, p 3 q and p 3 q . If and are nonzero complex numbers satisfying p and 3 3 q , then a quadratic equation having and as its roots is (A) ( p 3 q) x 2 ( p 3 2q) x ( p 3 q) 0 (B) ( p 3 q) x 2 ( p 3 2q) x ( p 3 q) 0 (C) ( p 3 q) x 2 (5 p 3 2q) x ( p 3 q) 0 (D) ( p 3 q) x 2 (5 p 3 2q) x ( p 3 q) 0 Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS Sol.: p …(i) 3 3 q …(ii) Sum of roots S 2 2 2 2 Product of roots P = 1 11 …(iii) From (i) and (ii) q p 2 2 2q p 3 p2 q p 2 3 3p S q p3 3p q p3 3p 3 p 3 2q 2 p 3 q p3 p 3 2q q p3 Required quadratic equation is x 2 Sx P 0 q p 3 x 2 p 3 2qx q p 3 0 Correct choice: (B) SECTION – II Multiple Correct Choice Type This section contains 5 multiple choice questions. Each question has four choices (A), (B), (C) and (D) for its answer, out of which ONE OR MORE may be correct. *37. Let ABC be a triangle such that ACB and let a, b and c denote the lengths of the sides opposite to A, B and C 6 respectively. The value(s) of x for which a x 2 x 1, b x 2 1 and c 2 x 1 is (are) (A) 2 3 Sol.: 2 (D) 4 3 2 x 2 x 1 x 2 1 2 x 12 6 2 x 2 x 1 x 2 1 2 3 x 2 3x 2x 2 x x 2 1 2 2x 2 x 1x 2 1 3 x 2 x 1 x 2x x 2 1 cos (C) 2 3 (B) 1 3 x 2 3 x 2 2 3 x 1 3 0 2 3 2 42 3 1 3 2 3 , 1 3 22 3 2 3 But x 2 3 (as a, b, c 0 x 1) Correct choice: (B) x 38. Let f be a real-valued function defined on the interval (0, ) by f ( x) ln x 1 sint dt . Then which of the following 0 statement(s) is (are) true? (A) f ' ' ( x) exists for all x (0, ) (B) f ' ( x) exists for all x (0, ) and f ' x is continuous on (0, ) , but not differentiable on (0, ) (C) there exists > 1 such that | f ' ( x) | | f ( x) | for all x (, ) (D) there exists > 0 such that | f ( x) | | f ' ( x) | for all x (0, ) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS Sol.: f x 12 1 1 sin x x Clearly f x exists and continuous for all x 0 . Also f x is not differentiable at point where sin x 1 . f x f x ln x 1 g x , where g x x x 1 sin t dt 1 sin x 0 x Now 1 sin t dt is always continuous, increasing and has range 0, . 0 So g x 0 for some k 0, as Also ln x 1 sin x 2 for x 0, 1 0 for x k , x y = lnx f x f x 0 for all x k k , y = 1/x f x f x for all x , , where k k k 1 Correct choice: (B), (C) *39. Let A and B be two distinct points on the parabola y 2 4 x . If the axis of the parabola touches a circle of radius r having AB as its diameter, then the slope of the line joining A and B can be (A) Sol.: 1 r (B) 1 r (C) 2 r (D) Let mid-point of AB is h, r 2 r B y2 = 4x xh yr Equation of AB is cos sin A So A and B can be cos h, sin r O C(h, ±r) x But these will satisfy y 2 4 x sin r 2 4 cos h 2 sin2 2 r sin 2 cos r 2 4h 0 Sum of roots = 0 AC CB r sin 2 cos tan 2 r Correct choice: (C), (D) Alternative: Slope of AB y 2 t1 t 2 B t22 , 2t2 t12 , 2t1 y-coordinate of mid-point of AB t1 t2 r A r x 2 2 slope of AB can be or r r 1 40. The value(s) of 0 22 (A) 7 x 4 (1 x) 4 1 x2 dx is (are) (B) 2 105 (C) 0 (D) 71 3 15 2 Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 1 Sol.: I x 4 1 x 2 2x 1 x 0 1 1 4 4 5 7 6 2 1 2 dx 1 x 4 1 x 2 dx 1 4x 5 dx 1 0 0 4 x 2 1 x 0 13 4x 6 1 x 2 dx 0 1 1 2 4 4 22 dx 4 5 7 3 5 3 7 x 1 1 2 Correct choice: (A) *41. Let Z1 and z 2 be two distinct complex numbers and let z (1 t ) z1 tz2 for some real number t with 0 t 1 . If Arg(w) denotes the principal argument of a nonzero complex number w, then (A) | z z1 | | z z 2 | | z1 z 2 | (B) Arg( z z1 ) Arg( z z 2 ) (C) Sol.: z z1 z z1 z 2 z1 z 2 z1 0 (D) Arg( z z1 ) Arg ( z 2 z1 ) Az1 , Bz , Cz 2 are collinear AB BC AC z z1 z z 2 z1 z 2 Argz z1 Argz z 2 Argz z1 Argz 2 z1 Equation of line A, B, C is z z1 z z1 z 2 z1 z 2 z1 0 Correct choice: (A), (C), (D) SECTION III Comprehension Type This section contains 2 paragraphs. Based upon the first paragraph 3 multiple choice questions and based upon the second paragraph 2 multiple choice questions have to be answered. Each of these questions has 4 choices (A), (B), (C) and (D) out of which ONLY ONE is correct. Paragraph for Questions 42 to 44 Let p be an odd prime number and T p be the following set of 2 × 2 matrices : a b Tp A : a, b, c {0, 1, 2, ....., p 1} c a 42. The number of A in T p such that A is either symmetric or skew-symmetric or both, and det (A) divisible by p is (B) 2( p 1) (A) ( p 1) 2 Sol.: (C) ( p 1) 2 1 (D) 2 p 1 For A to be symmetric b c a 2 b 2 should be multiple of p (a b) (a b) should be multiple of p Either (a b) or (a b) should be multiple of p a b can be multiple of p in ( p 1) ways (excluding a b 0 ) (a b) can be multiple of p in p ways (including a b 0 ) Total number of ways = 2p – 1 Correct choice: (D) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 43. 14 The number of A in T p such that the trace of A is not divisible by p but det (A) is divisible by p is [Note: The trace of a matrix is the sum of its diagonal entries.] (A) ( p 1)( p 2 p 1) Sol.: (B) p 3 ( p 1) 2 (C) ( p 1) 2 (D) ( p 1)( p 2 2) As tr A is not a multiple of p a0 a 2 bc will be a multiple of p if remainder of bc a2 and is same. p p Let when a 2 divided by p remainder is r when bc is divided by p for different values of c {0, 1,... p 1} we get distinct remainder {0, 1,... p 1} there exist only one value of b for which remainder of bc divided by p gives r a and c can be taken in ( p 1) ways each and b can be choose in only one way. Total ways ( p 1)2 1 Correct choice: (C) 44. The number of A in T p such that det (A) is not divisible by p is (B) p 3 5 p (A) 2 p 2 Sol.: The total number of A in T p p 3 (C) p 3 3 p (D) p 3 p 2 …(i) Now the A for which det A is divisible by p a0 Case-I: bc should be divisible by p either b 0 or c 0 or both total ways 2 p 1 Case-II: a0 Total ways ( p 1)2 [as in previous question] p 12 2 p 1 p 2 Total number of ways = Required ways = p3 p 2 …(ii) Correct choice: (D) Paragraph for Questions 45 to 46 The circle x 2 y 2 8x 0 and hyperbola *45. Equation of a common tangent with positive slope to the circle as well as to the hyperbola is (A) 2 x 5 y 20 0 Sol.: x2 y2 1 intersect at the points A and B. 9 4 (B) 2 x 5 y 4 0 (C) 3x 4 y 8 0 (D) 4 x 3 y 4 0 Let 41 cos, 4 sin be a point on the circle. Equation of tangent to the circle is x cos y sin 41 cos = 0 y x cos 41 cos sin sin …(i) Condition of tangency for hyperbola is c 2 a 2 m 2 b 2 Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 161 cos 2 2 sin 9 cos2 sin2 4 3 cos2 32 cos 20 0 2 and 10 (rejected) 3 cos sin 5 3 Slope of tangent from (i) is m = y 15 23 cos 2 sin 5 3 5 1 2 3 ; y 2 x 4 x 4 5 3 5 5 5 2 5 y 2x 4 2x 5 y 4 0 Correct choice: (B) *46. Sol.: Equation of the circle with AB as its diameter is (A) x 2 y 2 12x 24 0 (B) x 2 y 2 12x 24 0 (C) x 2 y 2 24x 12 0 (D) x 2 y 2 24x 12 0 y 2 8x x 2 x 2 8x x 2 1 9 4 4 x 2 72x 9 x 2 36 13x 2 72x 36 0 13x 2 78x 6 x 36 0 13xx 6 6( x 6) 0 x 6 , x6 13 Clearly 6, 0 is the centre. if x 6 , y 2 48 36 y 2 12 y 2 3 End points of diameter are 6, 2 3 , 6, 2 3 r 2 3 and C 6, 0 x 62 y 2 12 x 2 12x 36 y 2 12 x 2 y 2 12x 24 0 Correct choice: (A) SECTION IV Integer Answer Type This section contains TEN questions. The answer to each of the questions is a single-digit integer, ranging from 0 to 9. The correct digit below the question numbers in the ORS is to be bubbled. 47. Sol.: 2iˆ ˆj 3kˆ iˆ 2 ˆj If a and b are vectors in space given by a and b , then the value of 2a b . a b a 2b is 5 14 a 1, b 1 and a . b 0 2a b .[ a 2 2a . b b a . b 2 b 2 a] 1 0 2a . b b 2 0 2 2 a 2 a . b 1 4 5 Ans. 5 Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS *48. Sol.: The line 2 x y 1 is tangent to the hyperbola x2 y2 1 . If this line passes through the point of intersection of the a b2 nearest directrix and the x-axis, then the eccentricity of the hyperbola is y 2 x 1 …(i) y mx a 2 m 2 b 2 …(ii) 2 16 (i) and (ii) identical m 2 and 4a 2 b 2 1 Satisfying 2 x y 1 by 4a 2 e 2 2a 1 e …(iv) …(iii) Also b 2 a 2 e 2 1 b 2 a 2 e 2 a 2 …(v) From (iii) and (iv) b 2 e 2 1 e 2 1 a 2 e 2 1 a 1 e 2a e 2 Ans. 2 49. If the distance between the plane Ax 2 y z d and the plane containing the lines x 1 y 2 z 3 and 2 3 4 x2 y 3 z 4 is 6 , then | d | is 3 4 5 Sol.: Let d.c. of normal to the plane is l , m, n : 2l 3m 4n 0 3l 4m 5n 0 l m n 1 2 1 D.R. of normal to the plane is 1, 2, 1 Equation of plane is x 2 y z d Satisfying by 1, 2, 3 d 0 Required plane is x 2 y z 0 …(i) Given plane is Ax 2 y z d …(ii) From (i) and (ii) we get A 1 because planes are parallel. Now, d 0 6 d 6 12 2 2 12 Ans. 6 50. For any real number x, let [x] denote the largest integer less than or equal to x. Let f be a real valued function defined on the if [x] is odd, x [ x] 2 interval [–10, 10] by f ( x) . Then the value of 10 1 [ x] x if [x] is even 10 f ( x) cos x dx is 10 Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS Sol.: 17 Period of f x 2 Graph of f(x) Period of cos x 2 So, period of f x cos x 2 10 5.2 10 5.2 –5 –3 –2 –1 0 1 2 3 5 f x cos x dx f x cos x dx 2 10 f x cos x dx 0 2 2 1 1 10 f x cos x dx f x cos x dx 10 1 x cos x dx xcos x dx 1 1 0 0 1 2 x 1 cos x dx 0 1 10 1 x cos x dx 10 1 2 2 1 2 2 10 cos xdx x cos x dx x cos x dx cos x dx 10 0 0 2 2 0 1 1 0 40 2 2 So, 10 10 f x cos x dx 4 10 Ans. 4 51. Let be the complex number cos z 1 z 2 2 2 1 = 0 is equal to z 1 z 1 Sol.: Given determinant is 1 1 z By C1 C1 C2 C3 0 2 z z z 2 1 z 1 z 0 z 2 0 2 z 2 2 z 2 2 i sin . Then the number of distinct complex numbers z satisfying 3 3 1 0 2 1 2 z 2 2 0 z[ z 2 2 3] 0 z z 2 0 z 0 So number of solution is 1. Ans. 1 Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS *52. 18 Let Sk , k 1, 2,..., 100, denote the sum of the infinite geometric series whose first term is Then the value of 1002 100! k 100 2 k 1 1 and the common ratio is . k k! 3k 1 S k is k 1 k 1 1 k ! S for k 1 k 1 k 1 ! Rk k Ak Sol.: The value of 1002 100 ! k 2 3k 1S k 1002 100 100 ! k 1 S1 1 S 2 k 2 3k 1S k 100 k 3 1002 100 ! 100 0 1 k 1 k 2 ! k 1 ! k k 3 2 99 100 100 3 3 4 2 100 0 1 2 3 0 1 ........ 100 ! 99 ! 100 ! 1 ! 2 ! 2 ! 3 ! 98 ! 99 ! 1002 Ans. 3 53. The number of all possible values of , where 0 , for which the system of equations ( y z) cos3 ( xyz) sin3 ; 2 cos3 2 sin3 ; ( xyz) sin3 ( y 2z) cos3 y sin3 have a solution ( x0 , y0 , z0 ) with y0 z0 0 , is x sin3 y z Sol.: x sin3 1 1 cos3 cos3 0 y z x sin3 1 1 2 cos3 2 sin3 0 y z x sin3 1 1 2 cos3 cos3 sin3 0 y z sin3 cos3 cos3 2 sin3 0 The system of equations has solution, so sin3 2 cos3 sin3 2 cos3 cos3 sin3 1 cos3 cos3 2 sin3 0 sin3 1 2 cos3 0 0 cos3 sin3 sin3sin3 cos3cos3 0 sin3 0, cos3 0 , tan 3 1 1 But sin3 0 for sin3 0, 0 which is not possible y cos3 0 ( for cos3 0, 1 0 , not possible) z tan 3 1 ( for 3 solutions 5 3 , , ) 12 12 4 So number of solution = 3. Ans. 3 Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 54. Sol.: 19 Let f be a real-valued differentiable function on R (the set of all real numbers) such that f (1) 1 . If the y-intercept of the tangent at any point P( x, y) on the curve y f (x) is equal to the cube of the abscissa of P, then the value of f (3) is equal to dy According to given condition: y x x 3 dx xdy ydx xdx x2 But f 1 1 c y x2 y c d x dx x 2 x x3 3 x 3 The curve is y f 3 9 2 2 2 Ans. 9 *55. Sol.: n The number of values of in the interval , such that for n 0, 1, 2 and tan cot 5 as well as 5 2 2 sin2 cos 4 is tan cot 5 cos 6 0 6 n 2 …(i) 6 3 , 2 , , , , 2 as , 6 3, 3 2 2 2 2 2 2 2 2 Also sin 2 cos 4 cos 4 cos 2 4 2m 2 , m Z 2 2 6 2m or 2 2m 2 2 …(ii) From (i) and (ii) The number of common solution = 3 Ans. 3 Alternative: sin 2 cos 4 …(i) 2 sin2 2 sin 2 1 0 sin2 12 sin2 1 0 sin 2 1 or sin 2 1 2 , 2 , 2 2 5 , or 4 12 12 All the three values are satisfying the equation tan cot 5 Ans. 3 *56. The maximum value of the expression Sol.: Maximum value of the expression 1 sin 3sin cos 5 cos2 2 is 1 2 sin 3 sin cos 5 cos 2 1 1 1 2 5 3 3 sin 2 4 cos 2 3 1 sin 2 2 cos 2 1 3 2 2 2 min min Ans. 2 Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 20 SOLUTIONS TO IIT-JEE 2010 PHYSICS: Paper-I (Code: 8) PART – III SECTION – I Single Correct Choice Type This Section contains 8 multiple choice questions. Each question has four choices (A), (B), (C) and (D) out of which ONLY ONE is correct. 57. (A) IBL Sol.: A thin flexible wire of length L is connected to two adjacent fixed points and carries a current I in the clockwise direction, as shown in the figure. When the system is put in a uniform magnetic field of strength B going into the plane of the paper, the wire takes the shape of a circle. The tension in the wire is (B) T 2 dR ILB dR IBL T (C) IBL 2 (D) IBL 4 ILB 2 Correct choice: (C) 58. An AC voltage source of variable angular frequency and fixed amplitude V0 is connected in series with a capacitance C and an electric bulb of resistance R (inductance zero). When is increased (A) the bulb glows dimmer (B) the bulb glows brighter (C) total impedance of the circuit is unchanged (D) total impedance of the circuit increases 2 Sol.: 1 | Z | X C2 R 2 R2 C When angular frequency of the source increases the impedance of the circuit decreases, therefore the current in the circuit increases, hence the power through the resistance increases. Correct choice: (B) 59. To verify Ohm’s law, a student is provided with a test resistor RT , a high resistance R1 , a small resistance R2 , two identical galvanometers G1 and G2 , and a variable voltage source V. The correct circuit to carry out the experiment is G1 G1 R2 RT (A) R1 G2 R1 RT (B) V R1 R2 G1 RT G2 R2 V Sol.: R2 V G1 (C) G2 (D) RT G2 R1 V A galvanometer with a high resistance in series behaves as a voltmeter and a low resistance connected in parallel to the galvanometer behaves as an ammeter. Correct choice: (C) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 60. Incandescent bulbs are designed by keeping in mind that the resistance of their filament increases with the increase in temperature. If at room temperature, 100 W, 60 W and 40 W bulbs have filament resistances R100, R60, R40 respectively, the relation between these resistances is (A) Sol.: 21 1 1 1 R100 R40 R60 R (B) R100 R40 R60 (C) R100 R60 R40 (D) 1 1 1 R100 R60 R40 V2 , where R is the resistance at working temperature and not at room temperature P 1 1 1 R100 R60 R40 Correct choice: (D) *61. Sol.: A real gas behaves like an ideal gas if its (A) pressure and temperature are both high (C) pressure is high and temperature is low (B) pressure and temperature are both low (D) pressure is low and temperature is high Real gases behave like an ideal gas at very low densities. TR As P M0 P T Correct choice: (D) 62. Consider a thin square sheet of side L and thickness t, made of a material of resistivity . The resistance between two opposite faces, shown by the shaded areas in the figure is (A) directly proportional to L (B) directly proportional to t (C) independent of L (D) independent of t t L Sol.: R L L t t Correct choice: (C) *63. Sol.: A thin uniform annular disc (see figure) of mass M has outer radius 4R and inner radius 3R. The work required to take a unit mass from point P on its axis to infinity is (A) 2GM 4 2 5 7R (C) GM 4R (B) (D) P 4R 2GM 4 2 5 7R 2GM 5R 2 1 3R 4R Potential due to disc on its axis = 2G R 2 x 2 x (R is radius of disc, x is the distance from the centre of the disc on its axis) By superposition principle potential due to annular disc at point P, VP 2G R12 x 2 R22 x 2 W V VP As R1 4R, R2 3R , x 4R and Work done 2GM 4 2 5 7R M 4 R 3R 2 2 V 0 Correct choice: (A) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS *64. A block of mass m is on an inclined plane of angle . The coefficient of friction between the block and the plane is and tan . The block is held stationary by applying a force P parallel to the plane. The direction of force pointing up the plane is taken to be positive. As P is varied from P1 mg(sin cos ) to P2 mg(sin cos ) , the frictional force f versus P graph will look like f (B) P2 P1 P f (C) P f (A) P1 P2 P1 P2 P f (D) P1 P2 Sol.: 22 P P (i) when P mg sin P P f mg sin f tan > mgsin f mg sin P (ii) when P = mg sin , f = 0 (iii) when P mg sin P tan > f mg sin P mgsin f f P2 P1 P Correct choice: (A) SECTION – II Multiple Correct Choice Type This section contains 5 multiple choice questions. Each question has four choices (A), (B), (C) and (D) out of which ONE OR MORE may be correct. *65. A student uses a simple pendulum of exactly 1 m length to determine g, the acceleration due to gravity. He uses a stop watch with the least count of 1 sec for this and records 40 seconds for 20 oscillations. For this observation, which of the following statement(s) is (are) true? (A) Error T in measuring T, the time period, is 0.05 seconds (B) Error T in measuring T, the time period, is 1 second (C) Percentage error in the determination of g is 5% (D) Percentage error in the determination of g is 2.5% Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS Sol.: t = nT; T T t n t n T t l 4 2 n 2 l g ; 2 n g t2 Correct choices: (A), (C) 66. 23 1 0.05 sec. 20 g 2t 100 100 = 5% g t A ray OP of monochromatic light is incident on the face AB of prism ABCD near vertex B at an incident angle of 60° (see figure). If the refractive index of the material of the prism is 3 , which of the following is (are) correct? B O 600 (A) The ray gets totally internally reflected at face CD C 1350 P (B) The ray comes out through face AD (C) The angle between the incident ray and the emergent ray is 90° 900 (D) The angle between the incident ray and the emergent ray is 120° 750 D A Sol.: B sin 600 3 r = 300 sin r Let ic be the critical angle, then, sin i c 600 600 300 1 1350 C 450 450 3 300 < ic < 450 Also, the angle between incident and emergent ray is 90 0 300 750 Correct choices: (A), (B), (C) A 67. A few electric field lines for a system of two charges Q1 and Q2 fixed at two different points on the x-axis are shown in the figure. These lines suggest that (A) | Q1 | | Q2 | D 600 Q2 Q1 (B) | Q1 | | Q2 | (C) at a finite distance to the left of Q1 the electric field is zero (D) at a finite distance to the right of Q2 the electric field is zero Sol.: Number of field lines magnitude of charge and E KQ r2 Correct choices: (A), (D) *68. One mole of an ideal gas in initial state A undergoes a cyclic process ABCA, as shown in the figure. Its pressure at A is P0. Choose the correct option(s) from the following (A) Internal energies at A and B are the same (B) Work done by the gas in process AB is P0V0 n 4 (C) Pressure at C is Sol.: V0 P0 4 (D) Temperature at C is V B 4V0 C T0 4 A T0 T Process A B is isothermal, so WAB = P0V0 ln 4 and U AB = 0 Process B C is unknown (as its not given whether the line BC is directed towards origin or not) Correct choices: (A), (B) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 24 *69. A point mass of 1 kg collides elastically with a stationary point mass of 5 kg. After their collision, the 1 kg mass reverses its direction and moves with a speed of 2 ms–1. Which of the following statement(s) is (are) correct for the system of these two masses? (A) Total momentum of the system is 3 kg ms–1 (B) Momentum of 5 kg mass after collision is 4 kg ms–1 (C) Kinetic energy of the centre of mass is 0.75 J (D) Total kinetic energy of the system is 4 J Sol.: Applying conservation of linear momentum … (i) 1 V 5 0 1 2 5V2 1kg As collision is elastic, V2 2 V V 5kg 2m/s 1kg 5kg V2 After collision Before collision … (ii) V2 1 ms 1, V 3 ms 1 Total momentum of the system = 3 kg m/s Vcm 1 V 0 1 m/s 1 5 2 K . E cm 1 1 5Vcm2 0.75J 2 Correct choices: (A), (C) SECTION III Paragraph Type This section contains 2 paragraphs. Based upon the first paragraph 3 multiple choice questions and based upon the second paragraph 2 multiple choice questions have be answered. Each of these questions has four choices (A), (B), (C) and (D) out of which ONLY ONE is correct. Paragraph for Question Nos. 70 to 72 When a particle of mass m moves on the x-axis in a potential of the form V ( x) kx 2 , it performs simple harmonic motion. The corresponding time period is proportional to V(x) m , as can be seen easily using dimensional analysis. However, the motion of the k particle can be periodic even when its potential energy increases on both sides of x = 0 in a way different from kx2 and its total energy is such that the particle does not escape to infinity. Consider a particle of mass m moving on the x-axis. Its potential energy is V ( x) x 4 ( 0) for | x | near the origin and becomes a constant equal to V0 for V0 X0 | x | X 0 (see figure). *70. Sol.: If the total energy of the particle is E, it will perform periodic motion only if (A) E < 0 (B) E > 0 (C) V0 > E > 0 E V0 , E 0 Correct choice: (C) *71. For periodic motion of small amplitude A, the time period T of this particle is proportional to m Using dimensional analysis Correct choice: (B) (A) A Sol.: *72. 1 A m (C) A m (D) 1 A m The acceleration of this particle for | x | X 0 is (A) proportional to V0 Sol.: (B) (D) E > V0 (B) proportional to V0 mX 0 (C) proportional to V0 mX 0 (D) zero dU 0 dx Correct choice: (D) U V0 and F = Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 x ® IITJEE 2010 SOLUTIONS 25 Paragraph for Question Nos. 73 to 74 TC(B) Electrical resistance of certain materials, known as superconductors, changes abruptly from a nonzero value to zero as their temperature is lowered below a critical temperature TC (0). An interesting property of superconductors is that their critical temperature becomes smaller than TC (0) if they are placed in a magnetic field, i.e., the critical temperature TC (B) is a function of the magnetic field strength B. The dependence of TC (B) on B is shown in the figure. TC(0) B O 73. In the graphs below, the resistance R of a superconductor is shown as a function of its temperature T for two different magnetic field B1 (solid line) and B2 (dashed line). If B2 is larger than B1, which of the following graphs shows the correct variation of R with T in these fields? R R B2 (A) (B) B1 B1 B2 T O T O R R B1 (C) (D) B1 T O Sol.: B2 B2 O T Higher the magnetic field, lower is the temperature at which resistance abruptly becomes zero. Correct choice: (A) 74. A superconductor has TC (0) = 100 K. When a magnetic field of 7.5 Tesla is applied, its TC decreases to 75 K. For this material one can definitely say that when (A) B = 5 Tesla, TC (B) = 80 K (B) B = 5 Tesla, 75 K < TC (B) < 100 K (C) B = 10 Tesla, 75 K < TC (B) < 100 K (D) B = 10 Tesla, TC (B) = 70 K Sol.: As the magnetic field decreases, TC increases Correct choice: (B) SECTION IV Integer Type This section contains TEN questions. The answer to each question is a single-digit integer, ranging from 0 to 9. The correct digit below the question number in the ORS is to be bubbled. 75. When two identical batteries of internal resistance 1 each are connected in series across a resistor R, the rate of heat produced in R is J1. When the same batteries are connected in parallel across R, the rate is J2. If J1 = 2.25 J2 then the value of R in is Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS Sol.: 26 In first case 2 I R 2r r r 2 2 Rate of heat produced in R, J1 I 2 R R R 2r In second case I ' r R 2 Rate of heat produced in R, J 2 R As J 1 2.25J 2 I R r r 2 R r 2 I' R R 4r = 4 Answer is 4 *76. Two spherical bodies A (radius 6 cm) and B (radius 18 cm) are at temperatures T1 and T2, respectively. The maximum intensity in the emission spectrum of A is at 500 nm and in that of B is at 1500 nm. Considering them to be blackbodies, what will be the ratio of the rate of total energy radiated by A to that of B? Sol.: For a black body, energy radiated per unit time = AT 4 E A RA E B R B 2 TA T B (where R is radius of the body) 4 … (i) According to Wein’s displacement law, mT constant 2 4 E A 6 1500 =9 E B 18 500 Answer is 9 *77. When two progressive waves y1 4 sin(2 x 6t ) and y 2 3 sin 2 x 6t are superimposed, the amplitude of the 2 resultant wave is Sol.: 4 2 3 2 2 4 3 cos 25 5 2 A A12 A22 2 A1 A2 cos = Answer is 5 *78. A 0.1 kg mass is suspended from a wire of negligible mass. The length of the wire is 1 m and its cross-sectional areas is 4.9 × 10–7 m2. If the mass is pulled a little in the vertically downward direction and released, it performs simple harmonic motion of angular frequency 140 rad s–1. If the Young’s modulus of the material of the wire is n × 109 Nm–2, the value of n is Sol.: K m YA Lm 1402 YA n 10 n=4 4.9 107 1 0.1 9 Lm Answer is 4 Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS *79. 27 A binary star consists of two stars A (mass 2.2MS) and B (mass 11MS), where MS is the mass of the sun. They are separated by distance d and are rotating about their centre of mass, which is stationary. The ratio of the total angular momentum of the binary star to the angular momentum of star B about the centre of mass is Sol.: CM 2.2MS 11MS d/6 5d/6 L1 I 1 and L2 I 2 L1 I1 L2 I 2 11M S d / 62 2.2M S 5d / 62 6 2 11M S d / 6 Answers is 6 *80. Gravitational acceleration on the surface of a planet is earth. The average mass density of the planet is 6 g , where g is the gravitational acceleration on the surface of the 11 2 times that of the earth. If the escape speed on the surface of the earth is 3 taken to be 11 kms-1, the escape speed on the surface of the planet in kms–1 will be Sol.: VeP VeE M P RE P RP2 M E RP E RE2 As g RP g P E RE g E P VeP P E VeE E P VeP = 3 km/s … (i) GM 4 R3 g G R 2 3 R2 R … (ii) 2 gP g E 2 3 6 2 11 2 Answer is 3 *81. A piece of ice (heat capacity = 2100 J kg–1 °C–1 and latent heat = 3.36 × 105 J kg–1) of mass m grams is at –5°C at atmospheric pressure. It is given 420 J of heat so that the ice starts melting. Finally when the ice-water mixture is in equilibrium, it is found that 1 gm of ice has melted. Assuming there is no other heat exchange in the process, the value of m is Ans.: Heat required for melting ice = 1 3.36 105 336 J 100 Heat used for raising temperature of ice from (–50C to 00C) = Q 420 336 = 84 J Q msT 84 m 2100 5 m = 0.008 kg = 8 gm Answer is 8 *82. A stationary source is emitting sound at a fixed frequency f0, which is reflected by two cars approaching the source. The difference between the frequencies of sound reflected from the cars is 1.2% of f0. What is the difference in the speeds of the cars (in km per hour) to the nearest integer? The cars are moving at constant speeds much smaller than the speed of sound which is 330 ms–1. Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS Sol.: 28 V V0 Apparent frequency received by car is f1 f 0 V … (i) V The frequency of the reflected wave is f 1 ' f 1 V V0 V V0 = f0 V V 0 … (ii) Differentiating f 1 ' with respect to V0 660 f 0 2f df1 ' 330 V0 330 V0 f0 0 2 2 dV0 330 V0 330 V0 330 dV0 165df1 ' 7 km/h f0 Answer is 7 83. The focal length of a thin biconvex lens is 20 cm. When an object is moved from a distance of 25 cm in front of it to 50 cm, the magnification of its image changes from m25 to m50. The ratio Sol.: m25 is m5 0 1 1 1 V1 25 20 V1 100cm Similarly 1 1 1 52 3 V2 20 50 100 100 V2 100 cm 3 100 m 25 25 = 6 100 m50 3 50 Answer is 6 84. An -particle and a proton are accelerated from rest by a potential difference of 100V. After this, their de Broglie wavelengths are and p respectively. The ratio Sol.: p , to the nearest integer, is The momentum of a charged particle accelerated by potential difference V, P 2qmV de-Broglie wavelength, p h P 2 2e 4m V 2 2 3 2e m V Answer is 3 Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 29 ® SOLUTIONS TO IIT-JEE 2010 Paper-II (Code: 8) Please read the instructions carefully. You are allotted 5 minutes specifically for this purpose. A. General: 1. This Question Paper contains 24 pages having 57 questions. The question paper CODE is printed on the right hand top corner of this sheet and also on the back page of this booklet.. 2. No additional sheets will be provided for rough work. 3. Blank papers, clipboards, log tables, slide rules, calculators, cellular phones, pagers and electronic gadgets in any form are not allowed. 4. Log and Antilog tables are given in the paper. 5. The answer sheet, a machine-gradable Objective Response Sheet (ORS), is provided separately. 6. Write your Registration No., Name, Name of the centre and sign with pen in the appropriate boxes. Do not write these anywhere else. B. Question paper format and Marking scheme: 7. The question paper consists of 3 parts (Chemistry, Mathematics and Physics), and each Part consists of four Sections. 8. For each question in Section I, you will be awarded 5 marks if you have darkened only the bubble corresponding to the correct answer and zero mark if no bubbles are darkened. In all other cases, minus two (–2) mark will be awarded. 9. For each question in Section II, you will be awarded 3 marks if you darken only the bubble corresponding to the correct answer and zero mark if no bubble is darkened. No negative marks will be awarded for incorrect answers in this Section. 10. For each question in Section III, you will be awarded 3 marks if you darken only the bubble corresponding to the correct answer and zero mark if no bubbles are darkened. In all other cases, minus one (–1) mark will be awarded. 11. For each question in Section IV, you will be awarded 2 marks for each row in which you have darkened the bubble(s) corresponding to the correct answer. Thus, each question in this section carries a maximum of 8 marks. Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 30 SOLUTIONS TO IIT-JEE 2010 CHEMISTRY: Paper-II (Code: 8) PART – I SECTION – I Single Correct Choice Type This section contains 6 multiple choice questions. Each question has four choices (A), (B), (C) and (D) out of which ONLY ONE is correct. Note: Questions with (*) mark are from syllabus of class XI. O 1. In the reaction H3C– (1) NaOH/Br2 –C NH2 O (2) T –C Cl the structure of the Product T is O O H3C– –C (A) O–C (B) –NH C– O –CH3 O (C) H3C– (D) –NH –C H3C– O NH–C C– O O O Sol.: H3C– (1) NaOH/Br2 –C O –C Me– NH2 Cl –NH2 –HCl Me– –NH–C– Correct choice: (C) *2. Sol.: Assuming that Hund’s rule is violated, the bond order and magnetic nature of the diatomic molecule B 2 is (A) 1 and diamagnetic (B) 0 and diamagnetic (C) 1 and paramagnetic (D) 0 and paramagnetic Molecular orbital configuration of B2 as per the condition will be 1s2, *1s2, 2s2, *2s2, 2Py2 Bond order of B2 = 64 = 1. 2 B2 will be diamagnetic. Correct choice: (A) 3. The compounds P, Q and S COOH OCH3 O C O HO H3C P Q S were separately subjected to nitration using HNO3/H2SO4 mixture. The major product formed in each case respectively, is O COOH OCH3 C O (A) O2N HO H3C NO2 NO2 O COOH OCH3 C O (B) HO NO2 H3C NO2 NO2 Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS COOH O C OCH3 (C) HO H3C NO2 COOH O C OCH3 H3C NO2 CO2H NO2 O NO2 (D) HO 31 O NO2 NO2 CO2H HNO3/H2SO4 Sol.: NO2 OH OH (P) OCH3 HNO3/H2SO4 CH3 OCH3 NO2 CH3 (Q) O O HNO3/H2SO4 O O NO2 (S) Correct choice: (C) *4. The species having pyramidal shape is (A) SO3 Sol.: (B) BrF3 (C) SiO32 (D) OSF2 N 62 = = 4. 2 2 It has 1 lone pair. .. OSF2: O S F (Shape is trigonal pyramidal) F The shapes of SO3, BrF3 and SiO32 are triangular planar, T-shaped and triangular planar respectively. Correct choice: (D) 5. Sol.: The complex showing a spin-only magnetic moment of 2.82 B.M. is (A) Ni(CO)4 (B) [NiCl4]2– (C) Ni(PPh3)4 (D) [Ni(CN)4]2– Ni(CO)4 and Ni(PPh3)4 have Ni in zero oxidation state, while CO and Ph 3P are strong field ligands. Thus, both these molecules have sp3 hybridization and are diamagnetic. [Ni(CN)4]2– has electronic configuration of Ni2+ as 3d8 and hybridization is dsp2. It is diamagnetic. [NiCl4]2– has sp3 hybridization with 2 unpaired electrons giving spin only magnetic moment as 8 or 2.82 B.M. Correct choice: (B) 6. The packing efficiency of the two-dimensional square unit cell shown below is L (A) 39.27% (B) 68.02% (C) 74.05% (D) 78.54% Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS Sol.: Packing efficiency = = Area occupiedby effective circles Area of square 2r 2 2 L = 32 100 = 2r 2 (2 2 r ) 2 100 100 = 78.54%. 4 Correct choice: (D) SECTIONII Integer Type This section contains a group of 5 questions. The answer to each of the questions is a single digit integer, ranging from 0 to 9. The correct digit below the question no. in the ORS is to be bubbled. *7. One mole of an ideal gas is taken from a to b along two paths denoted by the solid and the dashed lines as shown in the graphs below. If the work done along the solid line path is ws and that along the dotted line path is wd, then the integer closest to the ratio wd/ws is 4.5 4.0 a 3.5 3.0 P 25 (atm) 2.0 1.5 1.0 0.5 b 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 V (lit.) Sol.: 3 5 2 5 wd = 4 11 = 6 1 2 3 3 2 wd = 26 L atm 3 5 .5 = –2.303 PV log 11 1/ 2 ws = –4.606 × 1.04 = –4.8 L atm 26 wd 3 = 1.80 ~ 2.0 = 4. 8 ws ws = –2.303 RT log The answer is 2. *8. Among the following, the number of elements showing only one non-zero oxidation state is Sol.: O, Cl, F, N, P, Sn, Tl, Na, Ti Fluorine generally shows O and –1 oxidation states while sodium shows 0 and +1 oxidation state. The answer is 2. 9. Sol.: Silver (atomic weight = 108 g mol–1) has a density of 10.5 g cm–3. The number of silver atoms on a surface of area 10–12 m2 can be expressed in scientific notation as y × 10x. The value of x is Silver has cubic close packed structure. It has fcc unit cell of edge length a cm. 4 108 10.5 = 6.0231023 (a ) 3 1/ 3 4 108 –8 a= = 4.087 × 10 cm. 23 6.02310 10.5 (i) Assuming that surface area given is the area of any extended face of a FCC unit cell. Area of square face = (4.087 × 10–8)2 cm2 2 Number of Ag atoms per unit area = 2 a Surface area = 10–12 m2 = 10–8 cm2. Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS Number of Ag atoms in the given surface area = 2 10 8 (4.08710 8 ) 2 33 = 1.197 × 107. x = 7. (ii) Assuming that surface area given is the area corresponding to closest packed layer. 2 a = 4r, r = 2 a 4.087108 2 = = 1.44 × 10–8 4 4 In a closest packed layer, the arrangement appears like 6 3 6 3 6 3 (2 × 1.44 × 10–8)2 = ( 2r ) 2 = 4 2.07 1016 4 4 4 = 21.5 × 10–16 cm2 Number of silver atoms on surface = 3 10 8 21.5 10 16 = 0.139 × 108 = 1.39 × 107. x = 7. The answer is 7. 10. Total number of geometrical isomers for the complex [RhCl(CO)(PPh 3)(NH3)] is Cl Sol.: PPh3 Rh Cl PPh3 Cl Rh Rh CO NH3 NH3 CO NH3 The number of geometrical isomers is 3. The answer is 3. *11. Sol.: CO PPh3 The total number of diprotic acids among the following is H3PO4 H2SO4 H3PO3 H2CO3 H3BO3 H3PO2 H2CrO4 H2SO3 H2S2O7 Diprotic acids are H2SO4, H3PO3, H2CO3, H2S2O7, H2CrO4 and H2SO3. The answer is 6. SECTION III Paragraph Type This Section contains 2 paragraphs. Based upon each of the paragraphs 3 multiple choice questions have to be answered. Each of these questions has four choices (A), (B), (C) and (D) out of which ONLY ONE is correct. Paragraph for questions 12 to 14 Two aliphatic aldehydes P and Q react in the presence of aqueous K2CO3 to give compound R, which upon treatment with HCN provides compound S. On acidification and heating, S gives the product shown below. H3C OH H3C O O Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 12. The compounds P and Q respectively are CH3 CH3 CH (A) C H3C H and H3C H (C) CH C CH3 O H and H3C H H (D) C O CH2 H3C H C O O CH3–CH–CHO + OH– CH3 H and C H3C O CH2 H3C CH (B) C O Sol.: 34 CH C CH3 O H and H H C O CH3–C––CHO + H2O CH3 (P) CH2O– CH2OH H2O – CH3–C –CHO + CH2 = O → CH3–C–CHO –OH– (Q) CH3 CH3 CH2OH CH2OH CH3–C–CH=O + HCN → CH3–C–CH–CN CH3 H3C OH (R) CH3–C–CHO CH3 CH2OH H+/H2O CH3–C–CH–COOH Intramolecular esterification H3C OH OH H3C H3C O O (S) Correct choice: (B) 13. The compound R is O O (A) H3C H3C C C H3C CH2 Sol.: Correct choice: (A) 14. The compound S is CH3 CH (C) H3C CH O C H CH CH O O (B) H H3C C CN CH2 CN CN CH OH (D) H3C CH OH C H3C OH H C H3C CH OH H3C OH CN CH2 Sol.: OH CH C CH3 CH (D) H3C H CH CH2 H CH3 C CH CH2 (A) H3C H3C O CH C C H3C OH CH3 (C) H3C (B) H CH2 OH Correct choice: (D) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 35 Paragraph for questions 15 to 17 The hydrogen-like species Li2+ is in a spherically symmetric state S1 with one radial node. Upon absorbing light the ion undergoes transition to a state S2. The state S2 has one radial node and its energy is equal to the ground state energy of the hydrogen atom. *15. Sol.: The state S1 is (A) 1s (B) 2s (C) 2p (D) 3s The spherically symmetric state S1 of Li2+ with one radial node is 2s. Upon absorbing light, the ion gets excited to state S 2, which also has one radial node. The energy of electron in S 2 is same as that of H-atom in its ground state En Z2 E1 where E1 is the energy of H-atom in the ground state n2 (3) 2 E1 for Li2+ n2 E n E1 n 3 State S2 of Li2+ having one radial node is 3p. Orbital angular momentum quantum number of 3p is 1. Energy of state S1 (3) 2 E1 2.25E1 (2) 2 Correct choice: (B) *16. Sol.: *17. Sol.: Energy of the state S1 in units of the hydrogen atom ground state energy is (A) 0.75 (B) 1.50 (C) 2.25 Correct choice: (C) (D) 4.50 The orbital angular momentum quantum number of the state S 2 is (A) 0 (B) 1 (C) 2 Correct choice: (B) (D) 3 SECTION IV (Matrix Type) This section contains 2 questions. Each question contains has four statements (A, B, C and D) given in Column I and five statements (p, q, r, s and t) in Column II. Any given statement in Column I can have correct matching with one or more statement(s) given in Column II. For example, if for a given question, statement B matches with the statements given in q and r, then for that particular question, against statement B, darken the bubbles corresponding to q and r in the ORS. 18. Match the reactions is Column I with appropriate options in Column II. Column I (A) –N2Cl + –OH Column II NaOH/H2O 0ºC –N=N– O OH OH (B) H3C–C–C–CH3 H3C CH3 H2SO4 C H3C (C) –C CH3 (D) HS– Sol.: –Cl 1. LiAlH4 2. H3O+ Base (p) Racemic mixture (q) Addition reaction (r) Substitution reaction (s) Coupling reaction (t) Carbocation intermediate CH3 C CH3 CH3 OH –CH CH3 O –OH S (A) – (r), (s) ; (B) – (t) ; (C) – (p), (q) ; (D) – (r) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 19. All the compounds listed in Column I react with water. Match the result of the respective reactions with the appropriate options listed in Column II. Column I Sol.: 36 Column II (A) (CH3)2SiCl2 (p) Hydrogen halide formation (B) XeF4 (q) Redox reaction (C) Cl2 (r) Reacts with glass (D) VCl5 (s) Polymerization (t) O2 formation (A) – (p), (s) Polymn. (CH3)2SiCl2 + 2H2O [(CH3)2Si–O]n. (CH3)2Si(OH)2 2 HCl (B) – (p), (q), (r), (t) XeF4 + H2O Xe + XeO3 + H2F2 + O2 SiO2 + 4HF SiF4 + 2H2O glass SiF4 + 2HF H2[SiF6] Soluble hexathorosilicic(IV) acid (C) – (p), (q) Cl2 + H2O HCl + HOCl (D) – (p), (q) VCl5 + 7H2O [V(H2O)6]3+ + 3Cl– + HCl + HOCl Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 37 SOLUTIONS TO IIT-JEE 2010 MATHEMATICS: Paper-II (Code: 8) PART – II SECTION – I Single Correct Choice Type This section contains 6 multiple choice questions. Each question has 4 choices (A), (B), (C) and (D) for its answer, out of which ONLY ONE is correct. x 20. Let f be a real-valued function defined on the interval (–1, 1) such that e x f ( x) 2 t 4 1 dt, for all x (1, 1), and 0 let f 1 be the inverse function of f . Then ( f (A) 1 Sol.: (B) e x f ( x) 2 1 )' (2) is equal to 1 3 (C) 1 2 (D) 1 e x t 4 1 dt …(i) 0 Putting x 0 f (0) 2 f 1 (2) 0 f ( f 1 ( x)) x f ' ( f 1 ( x)) . ( f 1 )' ( x) 1 ( f 1 )' (2) 1 f ' (0) Differentiate equation (i) with respect to x e x f ' ( x) e x f ( x) x 4 1 Putting x 0 f ' (0) 2 1 f ' (0) 3 (f 1 )' (2) 1 3 Correct choice: (B) 4 1 and respectively, is received by station A and then transmitted to 5 5 3 station B. The probability of each station receiving the signal correctly is . If the signal received at station B is green, then 4 the probability that the original signal was green is 3 6 20 9 (A) (B) (C) (D) 23 20 5 7 21. A signal which can be green or red with probability Sol.: RG Received signal is green OG Original signal was green If the event XYZ denotes original single sent to A was X, received at A was Y and received at B is Z O P G RG P(OG RG ) P(GRG) P(GGG) P ( R ) P(GRG) P(GGG) P( RRG) P( RGG) G 4 1 1 4 3 3 40 20 5 4 4 5 4 4 80 46 23 4 1 1 4 3 3 1 3 1 1 1 3 80 5 4 4 5 4 4 5 4 4 5 4 4 Correct choice: (C) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 22. If the distance of the point P(1, 2, 1) from the plane x 2 y 2 z , where 0 , is 5, then the foot of the perpendicular from P to the plane is 7 8 4 (A) , , 3 3 3 Sol.: 38 1 4 2 4 4 1 (B) , , 3 3 3 1 2 10 (C) , , 3 3 3 2 1 5 (D) , , 3 3 2 5 1 4 4 5 15 10 ( 0) P Plane is x 2 y 2 z 10 0 F Let the foot of perpendicular be F, equation of line PF is x 1 y 2 z 1 1 2 2 So the point F can be taken as ( 1, 2 2, 1 2) It will satisfy equation of plane. 1 4 4 2 4 10 0 5 3 7 8 4 Point F is , , 3 3 3 Correct choice: (A) *23. Let S {1, 2, 3, 4} . The total number of unordered pairs of disjoint subsets of S is equal to (A) 25 Sol.: (B) 34 (C) 42 (D) 41 Given set S 1, 2, 3, 4 For disjoint subsets A and B aS a A a A a A aB aB aB Then total number of disjoint subsets will be 34 1 1 = 41 2 Correct choice: (D) *24. For r 0, 1,.... 10 let Ar , Br and C r denote, respectively, the coefficient of x r in the expansions of (1 x)10 , (1 x) 20 and 10 (1 x) 30 . Then A (B r 10 Br C10 Ar ) is equal to r 1 2 (B) A10 ( B10 C10 A10 ) (A) B10 C10 10 Sol.: 2 10 20 C r C10 20 C r 30 C10 10 C r = r 1 = 20 C10 30 C10 1 30C10 20 C10 1 = 30 10 20 C10 (D) C10 B10 (C) 0 10 20 Cr C r 30C10 10 r 1 10 Cr 2 r 1 C10 20C10 C10 B10 Correct choice: (D) 25. Two adjacent sides of a parallelogram ABCD are given by AB 2iˆ 10 ˆj 11kˆ and AD iˆ 2 ˆj 2kˆ . The side AD is rotated by an acute angle in the plane of the parallelogram so that AD becomes AD' . If AD' makes a right angle with the side AB , then the cosine of the angle is given by (A) 8 9 (B) 17 9 (C) 1 9 (D) 4 5 9 Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS Sol.: D' AB . AD | AB | | AD | cos(90 ) 40 15 3 sin sin D 39 C 8 17 ; cos 9 9 90– A B Correct choice: (B) SECTION – II (Integer Type) This section contains 5 questions. The answer to each question is a single–digit integer, ranging from 0 to 9. The correct digit below the question no. in the ORS is to be bubbled. 26. 2k 1 2 k Let k be a positive real number and let A 2 k 1 2 k 2 k 0 2 k 2k and B 1 2k k 1 2k 1 k 0 2 k . 2 k 0 If det (adj A) det (adj B) 106 , then [k] is equal to [Note: adj M denotes the adjoint of a square matrix M and [k] denotes the largest integer less than or equal to k] Sol.: 2k 1 det A 0 2 k 2 k 2k 1 2k 1 2 k 2k 1 2k 1 0 2 k 1 2k 4 k 0 2k 1 2 k 1 2k 12k 12 8k 2k 13 1 detB 0 [ B is skew symmetric matrix of order 3] 2k 16 106 2k 1 10 k 9 [k] = 4 2 Ans. 4 27. Let f be a function defined on R (the set on all real numbers) such that f ' ( x) 2010( x 2009)( x 2010) 2 ( x 2011) 3 ( x 2012) 4 , for all x R . If g is a function defined on R with values in the interval (0, ) such that f ( x) ln(g ( x)) , for all x R , then the number of points in R at which g has a local maximum is Sol.: f x 1 . g x g x g x f x g x As g x 0 , So g x will change sign as – + 2009 + 2011 one point of maxima is x 2009 Ans. 1 *28. Let a1 , a2 , a3 ,.... a11 be real numbers satisfying a1 15 , 27 2a2 0 and ak 2ak 1 ak 2 for k 3, 4, ..., 11 . If 2 a a2 ... a11 a12 a22 ... a11 90 , then the value of 1 is equal to 11 11 Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS Sol.: 40 a1 15 As a k a k 1 a k 1 a k 2 So a1 , a 2 , a3 , ...... are in A.P. Also 27 2a 2 0 a 2 a1 3 3 d 2 2 2 11 a12 a 22 ...... a11 1 15 r 1d 2 90 90 11 11 r 1 225 150d 35d 2 90 7d 2 30d 27 0 But d Now 9 7 d 37d 9 0 d 3, 9 7 3 d 2 a1 a 2 ...... a11 1 1 30 10d 30 30 0 11 2 2 Ans. 0 29. Consider a triangle ABC and let a, b and c denote the lengths of the sides opposite to vertices A, B and C respectively. Suppose a 6 , b 10 and the area of the triangle is 15 3 . If ACB is obtuse and if r denotes the radius of the incircle of the triangle, then r 2 is equal to Sol.: 15 3 1 6 10 sin C 15 3 2 sin C cos C 3 2 C 3 2 36 100 c 2 120 C is obtuse c 14 Hence semi perimeter s 15 r 3 r2 3 Ans. 3 30. Two parallel chords of a circle of radius 2 are at a distance 3 1 apart. If the chords subtend at the center, angles of 2 , where k 0 , then the value of [k] is [Note : [k] denotes the largest integer less than or equal to k] k Sol.: p1 p 2 3 1 C D 2 cos 2 cos 3 1 k 2k /k 2 p1 O cos cos k 2k k 3 3 1 2 2 A /2k p2 B Ans. 3 Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 and k ® IITJEE 2010 SOLUTIONS 41 SECTION III (Paragraph Type) This section contains 2 paragraphs. Based upon each of the paragraphs 3 multiple choice questions have to be answered. Each of these question has four choices (A), (B), (C) and (D) out of which ONLY ONE is correct. Paragraph for Questions 31 to 33 Consider the polynomial f ( x) 1 2 x 3x 2 4 x 3 . Let s be the sum of all distinct real roots of f (x) and let t | s | . 31. The real number s lies in the interval 1 (A) , 0 4 Sol.: 3 (B) 11, 4 1 (D) 0, 4 1 3 (C) , 4 2 Given function f ( x) 1 2 x 3x 2 4 x 3 is monotonically increasing as f ' ( x) 2[6 x 2 3x 1] 0 x R 12[( x 1 / 4) 2 5 / 48] f (x) will have only one real root 3 1 Since f . f 0 4 2 1 3 s lies in , 2 4 Correct choice: (C) 32. The area bounded by the curve y f (x) and the lines x 0 , y 0 and x t , lies in the interval 3 (A) , 3 4 Sol.: 21 11 (B) , 64 16 21 (D) 0, 64 (C) (9, 10) 1 3 As t | s | t , 2 4 Hence required area will be the shaded region shown in the figure. –3/4 –1/2 O t t Area A(t ) (1 2 x 3x 2 4 x 3 ) dx t t 2 t 3 t 4 which is increasing 0 1 3 Area A , A 2 4 15 525 , 16 256 Correct choice: (A) 33. Sol.: The function f ' ( x) is 1 1 (A) increasing in t , and deceasing in , t 4 4 1 1 (B) decreasing in t , and increasing in , t 4 4 (C) increasing in (t , t ) (D) decreasing in (t , t ) 1 1 f x 24 x f x increases x , 4 4 1 f x decreases x , 4 Correct choice: (B) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 42 Paragraph for Questions 34 to 36 Tangents are drawn from the point P(3, 4) to the ellipse *34. Sol.: x2 y2 1 touching the ellipse at points A and B. 9 4 The coordinates of A and B are (A) (3, 0) and (0, 2) 8 2 161 and 9 , 8 (B) , 5 15 5 5 8 2 161 and (0, 2) (C) , 5 15 9 8 (D) (3, 0) and , 5 5 Let y mx 9m 2 4 be the tangent passing through point 3, 4 to the given ellipse. 4 3m2 9m 2 4 one tangent is y m 1 and indeterminate. 2 1 5 9 8 x at , and the other is x 3 at 3, 0 2 2 5 5 Correct choice: (D) *35. The orthocenter of the triangle PAB is 8 (A) 5, 7 Sol.: 7 25 (B) , 5 8 11 8 (C) , 5 5 8 7 (D) , 25 5 For othercentre of PAB . Altitude through B that is y 8 5 Correct choice: (C) *36. Sol.: The equation of the locus of the point whose distances from the point P and the line AB are equal, is (A) 9 x 2 y 2 6 xy 54x 62y 241 0 (B) x 2 9 y 2 6 xy 54x 62y 241 0 (C) 9 x 2 9 y 2 6 xy 54x 62y 241 0 (D) x 2 y 2 2 xy 27x 31y 120 0 Equation of AB is x 3 y 3 Required locus is 10 x 32 y 42 x 3 y 32 9 x 2 y 2 54x 62y 6 xy 241 0 Correct choice: (A) SECTION IV (Matrix Type) This section contains 2 questions. Each question has four statements (A, B, C and D) given in Column I and five statements (p, q, r, s and t) in Column II. Any given statement in Column I can have correct matching with one or more statement(s) given in Column II. For example, if for a given question, statement B matches with the statements given in q and r, then for that particular question, against statement B, darken the bubbles corresponding to q and r in the ORS Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS *37. 43 Match the statements in Column –I with those in Column-II. [Note : Here z takes values in the complex plane and Im z and Re z denote, respectively, the imaginary part and the real part of z]. Column I (A) Column II The set of points z satisfying z i | z | z i | z | is an ellipse with eccentricity (q) the set of points z satisfying Im z = 0 1 is w (r) the set of points z satisfying | Im z| 1 1 is w (s) the set of points z satisfying | Re z| 2 (t) the set of points z satisfying | z | 3 contained in or equal to (B) The set of points z satisfying z 4 z 4 10 is contained in or equal to (C) If | w | 2 , then the set of points 4 5 (p) z w contained in or equal to (D) If | w | 1 , then the set of points z w contained in or equal to Sol.: (A) – (q), (r); (B) – (p); (C) – (p), (s), (t); (D) – (q), (r), (s), (t) (A) z is purely real Im z = 0 (B) z is on ellipse (C) z x2 y2 1 25 9 3 5 cos i sin 2 2 Also represents ellipse (D) 38. 3 5 | z | 2 2 4x 2 4 y 2 4 1 , whose eccentricity = 9 25 5 z 2 cos Match the statements in Column –I with the values in Column-II. Column I (A) A line from the origin meets the lines Column II x 2 y 1 z 1 and 1 2 1 8 3 y 3 z 1 at P and Q respectively. If length PQ d , then 2 1 1 x (p) –4 d 2 is (B) 3 The values of x satisfying tan 1 ( x 3) tan 1 ( x 3) sin1 are 5 (q) 0 (C) Non-zero vectors a , b and c satisfy a . b 0 , (b a ) . (b c ) 0 and 2 | b c | | b a | . If a b 4c , then the possible values of are (r) 4 (s) 5 (t) 6 (D) Let f be the function on [–, ] given by 2 9x x f ( x) sin / sin for x 0 . The value of 2 2 f (0) 9 f ( x) dx is and Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS Sol.: (A) 44 8 Let P 2, 2 1, 1 and Q 2 , 3, 1 3 Now 2 2 1 1 8 3 1 2 3 3 4 P O 7 26 3 3 …(i) 2 …(ii) 5 14 4 3 3 …(iii) From (i) and (ii) 16 44 4 3 3 …(iv) 8 20 4 3 3 …(v) From (ii) and (iii) Q 1 3 On solving (iv) and (v) 3, 10 10 4 Hence P 5, 5, 2 and Q , , 3 3 3 d2 25 25 4 =6 9 9 9 (t) is correct. (B) tan 1 x 3 tan 1 x 3 sin1 3 5 6 6 3 3 tan 1 tan 1 tan 1 tan 1 8 x 2 8 x 4 2 2 4 4 1 x 9 x 8 (p) and (r) are correct. (C) b a. b c 0 a b a b a 0 b 2 b.c a.c 0 b 2 b . 4 4 a2 0 4 b 2 a 2 b2 b2 4 4 Also 2 b c b a a b 2 b b a 4 4 2 b 2 a 2 4b 2 a 2 Diving (i) and (ii) 4 4 2 4 4 b a …(i) 2 b a 4 2 4b 2 3a 2 …(ii) 1 12 3 16 2 8 4 5 2 0 3 5 as it doesnot satisfy equation(i) and ii (q) is correct. Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS (D) I 2 sin 9 x 2 dx x sin 0 2 9 9 x cos 9 x 2 2 2 I 2 dx 2 dx cos x 2 x sin 0 0 2 2 sin 9x x 2 2 sin 5 x 2 cos x sin 5 x sin 5 x 2 2 2I 2 2 dx 4 4 2 dx 8 x x sin x 2 sin x cos x sin x 0 2 sin cos 0 0 0 2 2 sin 2 2 2 2 1 cos 4 x dx sin 4 x sin6 x 2 I 4 dx dx 4 3 4 sin 2 x dx 4 3 4 sin 2 x 2 sin 2 x 0 0 0 0 2 2 I 4 1 dx 8 0 I cos 4 x dx 4 8 2 2 0 4 cos 4x dx 0 4 2 I1 2 4 4 2 (r) are correct. Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 45 ® IITJEE 2010 SOLUTIONS 46 SOLUTIONS TO IIT-JEE 2010 PHYSICS: Paper-II (Code: 8) PART – III SECTION – I Single Correct Choice Type This section contains 6 multiple choice questions. Each question has four choices (A), (B), (C) and (D) out of which ONLY ONE is correct. 39. A biconvex lens of focal length 15 cm is in front of a plane mirror. The distance between the lens and the mirror is 10 cm. A small object is kept at a distance 30 cm from the lens. The final image is (A) virtual and at a distance of 16 cm from the mirror (B) real and at a distance of 16 cm from the mirror (C) virtual and at a distance of 20 cm from the mirror (D) real and at a distance of 20 cm from the mirror Sol.: First image will be formed by lens, Using lens formula 1 1 1 1 1 1 v 30 cm v u f v 30 15 This image will act as virtual object for mirror and second image will be formed at 20 cm in front of mirror. This image will act as virtual object for lens and final image will be formed at 1 1 1 1 1 1 v 6 cm from lens. v u f v 10 15 This image is real and at a distance of 16 cm in front of mirror. Correct choice: (B) 40. O 30cm A uniformly charged thin spherical shell of radius R carries uniform surface charge density per unit area. It is made of two hemispherical shells, held together by pressing them with force F (see figure). F is proportional to (A) Sol.: f =15cm 1 2 2 R 0 F (B) 1 2 R 0 (C) F F 1 2 0 R (D) 1 2 0 R 2 2 R 2 2 0 2 R2 0 Correct choice: (A) F *41. 10cm Fe F A block of mass 2 kg is free to move along the x-axis. It is at rest and from t = 0 onwards it is subjected to a time-dependent force F(t) in the x direction. The force F(t) varies with t as shown in the figure. The kinetic energy of the block after 4.5 seconds is (A) 4.50 J (B) 7.50 J (C) 5.06 J (D) 14.06 J F(t) 4N 4.5s O Sol.: 3s Area under F-t graph = Change in momentum of body 1 1 4 p 4 3 1.5 1.5 = 4.5 kg m s–1 2 2 3 p2 k 5.06 J 2m Correct choice: (C) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 t ® IITJEE 2010 SOLUTIONS *42. Sol.: 47 A hollow pipe of length 0.8 m is closed at one end. At its open end a 0.5 m long uniform string is vibrating in its second harmonic and it resonates with the fundamental frequency of the pipe. If the tension in the wire is 50 N and the speed of sound is 320 ms–1, the mass of the string is (A) 5 grams (B) 10 grams (C) 20 grams (D) 40 grams VS 2V 4L p 2l l (VS = velocity of sound) 320 1 T 4 0.8 0.5 = 0.02 kg m–1 m = l = 10 grams 0.8m Correct choice: (B) *43. A Vernier calipers has 1 mm marks on the main scale. It has 20 equal divisions on the Vernier scale which match with 16 main scale divisions. For this Vernier calipers, the least count is (A) 0.02 mm (B) 0.05 mm (C) 0.1 mm (D) 0.2 mm Sol.: 1 VSD 16 MSD 20 Least count = 1 MSD – 1 VSD = 1 mm – 0.8 mm = 0.2 mm Correct choice: (D) *44. A tiny spherical oil drop carrying a net charge q is balanced in still air with a vertical uniform electric field of strength 81 105 Vm 1 . When the field is switched off, the drop is observed to fall with terminal velocity 2 × 10 –3 m s–1. Given g = 7 9.8 m s–2, viscosity of the air = 1.8 × 10–5 Ns m–2 and the density of oil = 900 kg m–3, the magnitude of q is (A) 1.6 × 10–19 C (B) 3.2 × 10–19 C (C) 4.8 × 10–19 C (D) 8.0 × 10–19 C Sol.: For equilibrium, qE = mg q 4r 3g 3E … (i) Also, mg = 6rv 4 3 r g 6 r v 3 (after field is switched off) … (ii) From equation (i) and (ii) q = 8.0 × 10–19 C Correct choice: (D) SECTION – II Integer Type This section contains 5 questions. The answer to each question is a single-digit integer, ranging from 0 to 9. The correct digit below the question number in the ORS is to be bubbled. 45. To determine the half life of a radioactive element, a student plots a dN (t ) dN (t ) graph of n versus t. Here is the rate of radioactive dt dt decay at time t. If the number of radioactive nuclei of this element decreases by a factor of p after 4.16 years, the value of p is 6 5 ln dN t 4 dt 3 2 1 2 3 4 5 6 7 8 Years Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS Sol.: 48 d N t d N t N 0 e t , ln lnN 0 t dt dt 1 1 Comparing with y mx C , we get (from the graph, year1 |slope of graph|) 2 2 N t N 0 e t , N N 0 t t 1 T1 / 2 2 1 1 ln 2 p 2 4.16 1 1 20.693 p 2 Answer is 8 p=8 46. Image of an object approaching a convex mirror of radius of curvature 20 m along its optical axis is observed to move from 25 50 m to m in 30 seconds. What is the speed of the object in km per hour? 3 7 Sol.: By mirror formula R=20m 2 1 1 R v u V t =30s Initially at t = 0 t=0 50/7m I 25/3m 2 1 1 u1 50 m 20 25 / 3 u1 I Finally at t = 30s 2 1 1 u 2 25m 20 50 / 7 u 2 velocity of object | u 2 u1 | 3 kmh 1 t Answer is 3 47. Sol.: A large glass slab ( = 5/3) of thickness 8 cm is placed over a point source of light on a plane surface. It is seen that light emerges out of the top surface of the slab from a circular area of radius R cm. What is the value of R? sinic 1 sinic R 1 3 5 R 3 tan ic 8 cm 4 =5/3 ic = 37° R = 6 cm ic ic 8cm Source Answer is 6 48. At time t = 0, a battery of 10 V is connected across points A and B in the given circuit. If the capacitors have no charge initially, at what time (in seconds) does the voltage across them become 4 V? (Take: ln 5 = 1.6, ln 3 = 1.1) 2M A B 2M Sol.: 2F 2F In the given figure, Req = 1 M, Ceq = 4 F Time constant = ReqCeq = 4 sec t Potential across the equivalent capacitor at any time t is V V0 1 e 4 10 1 e t / 4 t ln5 ln3 t = 2 s 4 Answer is 2 Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 49 1 of its initial volume. If the initial temperature of the gas is Ti 32 (in Kelvin) and the final temperature is aTi, the value of a is *49. A diatomic ideal gas is compressed adiabatically to Sol.: For adiabatic process TV –1 = constant TiVi –1 = TfVf –1 V T f Ti i Vf 1 4 Ti [ = 7/5 for a diatomic gas] a=4 Answer is 4 SECTION III Paragraph Type This section contains 2 paragraphs. Based upon the paragraph 3 multiple choice questions have to be answered. Each of these questions has four choices (A), (B), (C) and (D) out of which ONLY ONE is correct. Paragraph for Question Nos. 50 to 52 When liquid medicine of density is to be put in the eye, it is done with the help of a dropper. As the bulb on the top of the dropper is pressed, a drop forms at the opening of the dropper. We wish to estimate the size of the drop. We first assume that the drop formed at the opening is spherical because that requires a minimum increase in its surface energy. To determine the size, we calculate the net vertical force due to the surface tension T when the radius of the drop is R. When this force becomes smaller than the weight of the drop, the drop gets detached from the dropper. *50. If the radius of the opening of the dropper is r, the vertical force due to the surface tension on the drop of radius R (assuming r << R) is (A) 2 rT Sol.: (B) 2 RT (C) 2r 2T R (D) 2R 2T r Force due to surface tension = T 2r cos = T 2r r 2r 2T R R Correct choice: (C) r R *51. Sol.: If r = 5 × 10–4 m, = 103 kgm–3, g = 10 ms–2, T = 0.11 Nm–1, the radius of the drop when it detaches from the dropper is approximately (A) 1.4 × 10–3 m (B) 3.3 × 10–3 m (C) 2.0 × 10–3 m (D) 4.1 × 10–3 m 4 mg R 3 g 3 r2 4 3 2 T 2 T R 3 g r R4 R 3 2 g 3 T 4.1251012 Substituting the values, R 4 r 2 g 2 4 log10 R 12 log10 4.125 4 log10 R 12 0.6154 log R 2.8462 log10 R 3 0.1538 R = 1.425 10–3 m Correct choice: (A) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS *52. Sol.: After the drop detaches, its surface energy is (A) 1.4 × 10–6 J (B) 2.7 × 10–6 J (C) 5.4 × 10–6 J 50 (D) 8.1 × 10–6 J US = T × 4R2 = 0.11 × 4 × R2 = 2.7 × 10–6 J Correct choice: (B) Paragraph for Question Nos. 53 to 55 The key feature of Bohr’s theory of spectrum of hydrogen atom is the quantization of angular momentum when an electron is revolving around a proton. We will extend this to a general rotational motion to find quantized rotational energy of a diatomic molecule assuming it to be rigid. The rule to be applied is Bohr’s quantization condition. 53. A diatomic molecule has moment of inertial I. By Bohr’s quantization condition its rotational energy in the nth level (n = 0 is not allowed) is (A) Sol.: 1 h 2 n 2 8 2 I L I nh 2 (B) K 1 h 2 n 8 2 I h2 (C) n 2 8 I h2 (D) n 2 2 8 I h2 L2 n2h2 2 n2 2 8 I 2 I 4 2 I Correct choice: (D) 54. It is found that the excitation frequency from ground to the first excited state of rotation for the CO molecule is close to 4 1011 Hz . Then the moment of inertia of CO molecule about its center of mass is close to (Take h = 2 × 10–34 J s) (A) 2.76 × 10–46 kg m2 (B) 1.87 × 10–46 kg m2 (C) 4.67 × 10–47 kg m2 (D) 1.17 × 10–47 kg m2 Sol.: E hv K K 2 K 1 h2 8 I 2 2 12 E K hv I 3h 2 8 2 I 3h 8 2 v 1.87 1046 kgm2 Correct choice: (B) 55. In a CO molecule, the distance between C (mass = 12 a.m.u.) and O (mass = 16 a. m. u), where 1 a. m. u. close to (A) 2.4 × 10–10 m Sol.: (B) 1.9 × 10–10 m (C) 1.3 × 10–10 m 5 1027 kg , is 3 (D) 4.4 × 10–11 m I d 2 , where is reduced mass m mo I c mc mo 2 d d 1.3 1010 m Correct choice: (C) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 51 SECTION IV (Matrix Type) This section contains 2 questions. Each question has four statements (A, B, C and D) given in Column I and five statements (p, q, r, s and t) in Column II. Any given statement in Column I can have correct matching with one or more statement(s) given in Column II. For example, if for a given question, statement B matches with the statements given in q and r, then for that particular question, against statement B, darken the bubbles corresponding to q and r in the ORS. 56. Two transparent media of refractive indices 1 and 3 have a solid lens shaped transparent material of refractive index 2 between them as shown in figure in Column II. A ray traversing these media is also shown in the figures. In Column I different relationships between 1, 2 and 3 are given. Match them to the ray diagrams shown in Column II. Column I (A) (B) Column II 1 2 (p) 3 (q) 3 2 1 1 2 (C) 2 3 2 3 1 1 (r) 2 (D) 2 3 (s) 3 2 1 (t) 3 Ans.: 2 1 (A) – (p), (r) ; (B) – (q), (s), (t) ; (C) – (p), (r), (t) ; (D) – (q), (s) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS 57. 52 You are given many resistances, capacitors and inductors. These are connected to a variable DC voltage source (the first two circuits) or an AC voltage source of 50 Hz frequency (the next three circuits) in different ways as shown in Column II. When a current I (steady state for DC or rms for AC) flows through the circuit, the corresponding voltage V1 and V2. (indicated in circuits) are related as shown in Column I. Match the two Column I Column II V1 (A) I 0, V1 is proportional to I V2 6mH 3F (p) V (B) I 0, V2 V1 (q) V1 V2 6mH 2 V (C) V1 0, V2 V (r) V1 V2 6mH 2 ~ V V1 (D) I 0, V2 is proportional to I (s) V2 6mH 3F ~ (t) V2 1k 3F ~ Sol.: V V1 V (A) – (r), (s), (t) ; (B) – (q), (r), (s), (t) ; (C) – (p), (q) ; (D) – (q), (r), (s), (t) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 ® IITJEE 2010 SOLUTIONS BREAK UP 1 (LEVEL OF DIFFICULTY) BREAK UP 1 (LEVEL OF DIFFICULTY) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 53 ® IITJEE 2010 SOLUTIONS Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 54 ® IITJEE 2010 SOLUTIONS BREAK UP 1 (LEVEL OF DIFFICULTY) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 55 ® IITJEE 2010 SOLUTIONS BREAK UP 2 (XI-XII) BREAK UP 2 ( XI-XII) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 56 ® IITJEE 2010 SOLUTIONS Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 57 ® IITJEE 2010 SOLUTIONS BREAK UP 2 (XI-XII) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 58 ® IITJEE 2010 SOLUTIONS BREAK UP 3 (TOPICWISE/PARTWISE) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 59 ® IITJEE 2010 SOLUTIONS BREAK UP 3 (TOPICWISE/PARTWISE) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 60 ® IITJEE 2010 SOLUTIONS BREAK UP 3 (TOPICWISE/PARTWISE) Brilliant Tutorials Pvt. Ltd. Head Office: 12, Masilamani Street, T. Nagar, Chennai-600 017 Delhi Office: 50-C, Kalu Sarai (Behind Azad Apartments), New Delhi-110 016 Ph.: 2653 7392/93/94/95 Fax: 2653 7396 61