XII - Govind Vidyalaya

Transcription

STD XII
BLUE PRINT OF PHYSICS- FIRST TERM-2015
CHAPTER
ELECTROSTATICS
CURRENT
ELECTRICITY
MAGNETIC
EFFECTOF
CURRENT&
MAGNETISM
EMI & A.C
EMW
(a)
(b)
(c)
(d)
(e)
VSA
(1
Marks)
1X8=8
2
3
SA-1
(2 Marks)
2X10=20
SA-II
(3 Marks)
3X8=24
VBQ
(3 Marks)
1X3=3
2
3
2
2
1
17
15
1
2
2
1
16
2
1
2
1
2
16
06
1
L.A
(5 Marks)
3X5=15
TOTAL
70 Marks
GENERAL INSTRUCTION FOR ALL SET
All questions are compulsory.
There are 30 questions in total. Questions 1 to 8 carry one mark each, questions 9 to 18 carry
two marks each, questions 19 to 27 carry three marks each and questions 28 to 30 carry five
marks each.
There is no overall choice. However, an internal choice has been provided in all three questions
of five marks each. You have to attempt only one of the given choices in such questions.
Use of calculators is not permitted.
You may use the following physical constants wherever necessary :
c = 3 × 𝟏𝟎𝟖 m/s
h = 6.63 × 𝟏𝟎−𝟑𝟏 Js
e = 1.6 × 𝟏𝟎−𝟏𝟗 C
𝝁𝟎 = 4π × 𝟏𝟎−𝟕 T m𝑨−𝟏
𝟏
= 9 × 𝟏𝟎𝟗 N 𝒎𝟐 𝑪−𝟐
𝟒𝝅𝜺
𝟎
Mass of electron = 9.1 × 𝟏𝟎−𝟑𝟏 kg
Mass of Neutron= 1.675 × 𝟏𝟎−𝟐𝟕 kg
Mass of proton = 1.673 × 𝟏𝟎−𝟐𝟕 kg
GOVIND VIDYALAYA TAMULIA
XII – PHYSICS
SET NO-01
Time : 3 Hours
Max. Marks : 70
1. Charges of magnitude 2Q and –Q are located at points (a, o, o ) and (4a, o, o) Find the ratio of
the flux of electric field, due to these charges, through concentric spheres of radii 2a & 8a
centered at the origin.
2. Two charges 5nC and -2nC are placed at points (5cm, 0, 0) and (23cm, 0, 0) on a region of
space where there is no other external field. Calculate the electrostatic potential energy of this
charge system.
3. Explain, with the help of graph, the variation of conductivity with temperature for a metallic
conductor.
4. Electrons are continuously in motion within a conductor but there is no current in it unless
some source of potential is applied across its ends. Give reason.
5. A current is passed through a steel wire heating it to red hot. Then half of the wire is
immersed in cold water. Which half of the wire will heat up more and why?
6.A charged particle of mass 5 mg and charge q = 2 μC has velocity v= 2i – 3j + 4k. Find out the
magnetic force on the charged particle and its acceleration at this instant due to the magnetic
field B = 3j – 2k. B and v are in Wb/sq. m and m/s respectively.
7. A variable frequency a.c source is connected to a capacitor. Will the displacement current
increase or decrease with increasing frequency?
8. The amplitude of harmonic electromagnetic wave in vacuum is Bo =510 n T. What is the
amplitude of the electric field part of the wave?
9. A slab of material of dielectric constant K has the same areas as the plates of parallel plate
3
capacitor, but has a thickness(5 𝑑), where d is the separation of the plates, how is the capacitance
change when the slab is inserted between the plates ?
10. The battery remains connected to a parallel plate capacitor and a dielectric slab is inserted between
the plates. What will be the effect on its - (i) Capacity (ii) Charge
(iii) Potential difference
(iv) Energy stored ?
11. Derive an expression for drift velocity of free electrons in a conductor in terms of relaxation
time.
12. The sequence of coloured bands in two carbon resistor R1 and R2 is
a) brown, green, blue and
b) orange, black, green.
Find the ratio of their resistances.
13. On what factors, does the potential gradient of the potentiometer wire depend?
14.
15.
16.
17.
18. State two application of infrared radiation.
19. Figure shows two identical capacitance C1 and C2 each of the 1𝜋𝐹 capacitance connected to a
battery of 6V. Initially switch ‘S’ is closed. After sometime S is left open and dielelctric slabs of
dielectric constant K = 3 are inserted to fill completely the space between the plates of the two
capacitors. How will the (i) Charge and (ii) Potential difference between the plates of the capacitors
be affected after the slabs are inserted.
20.
A test charge ‘q’ is moved without acceleration from A to C along the path from A to B and
then from B to C in electric field E as shown in figure B to C in electric field E as shown in figure.
a) Calculate the potential difference between A and C.
b) At which point (of the two) is the electric potential more and why ?
21. The potential difference across terminals of a cell were measured (in V) against different currents
(In A) flowing through the cell. A graph was drawn which was a straight line ABC. Using the data
given in the graph determine i) The emf and ii) The internal resistance of the cell.
22.
Derive an expression for the drift speed of electrons in a good conductor in terms of the
relaxation time of electrons.
23.
24. Explain with the help of a neat diagram the principle and working of a moving coil Galvanometer
25.
26.
27.Renu, Ritu and Kajal lived in a resettlement colony where they observed most houses stole
power from transmission lines using hooks. They had learnt in school about fire caused due to
electric short circuit. They decided to make people aware of the risks involved and also the
importance of paying their electricity bills. They got all their friends and responsible elders together
and with the help of the electricity board, succeeded in changing the situation.
a) What values did Renu, Ritu and Kajal have?
b) A low voltage supply from which one needs high currents must have a very low internal
resistance, why?
c) A high tension supply of say 6 KV must have a very large internal resistance. Why?
28.
OR
(a) Define electric flux. Write its S.I. unit.
(b) Using Gauss's law, prove that the electric field at a point due to a uniformly charged infinite plane
sheet is independent of the distance from it.
(c) How is the field directed if (i) the sheet is positively charged,(ii) negatively charged
29. (i)What is the relationship between the current and the magnetic moment of a current carrying
circular loop? Use the expression to derive the relation between the magnetic moment of an electron
moving in a circle and its related angular momentum?
(ii)A muon is a particle that has the same charge as an electron but is 200 times heavier than it. If we
had an atom in which the muon revolves around a proton instead of an electron, what would be the
magnetic moment of the muon in the ground state of such an atom?
OR
(i) Describe an expression for the magnetic field at a point on the axis of a current carrying circular
loop.
(ii) Two coaxial circular loops L1 and L2 of radii 3cm and 4cm are placed as shown. What should be
the magnitude and direction of the current in the loop L2 so that the net magnetic field at the point O
be zero?
OR
30.
XII – PHYSICS
SET N0-02
Time : 3 Hours
Marks : 70
Max.
1. Draw the graph showing the variation of electric potential with distance from the centre of a
uniformly charged shell.
2. Find the ratio of the electric field lines starting from a proton kept first in vacuum and then in a
medium of dielectric constant 6.
3. How does the drift velocity of electrons in a metallic conductor vary with increase in temperature?
4. Two different wires X and Y of same diameter but of different materials are joined in series and
connected across a battery. If the number density of electrons in X is twice that of Y, find the ratio of
drift velocity of electrons in the two wires.
5.
6. In a certain arrangement, a proton does not get deflected while passing through a magnetic field
region. State the condition under which it is possible.
7. Name the Maxwell’s equation among the four which shows that the magnetic monopole does not
exist?
8. Give reason for decrease or increase in velocity of light, when it moves from air to glass or glass
to air respectively?
9. Two uniformly large parallel thin plates having charge densities + 𝜎 and - 𝜎 are kept in the x-z plane
at a distance ‘d’ apart. Sketch an equipotential surface due to electric field between the plates. If a
particle of mass ‘m’ and charge ‘-q’ remains stationary between the plates what is the magnitude
and direction of this field.
10. A charge ‘Q’ located at a point → is in equilibrium under the combined electric field of three
𝑟
charges q1, q2, q3. If the charges q1, q2 are located at points → and → respectively, find the
𝑟1
𝑟2
direction of the force on Q. Due to q3 in term of q1, q2, →, → and →
𝑟1 𝑟2
𝑟
11. Derive an expression for the resistivity of a good conductor, in terms of the relaxation time of
electrons.
12. Write the mathematical relation between mobility and drift velocity of charge carriers in a
conductor. Name the mobile charge carriers responsible for conduction of electric current in (a)
an electrolyte (b) and ionized gas.
13. A 10 m long wire of resistance 20Ω is connected in series with a battery of Emf 3 V (negligible
internal resistance) and a resistance of 10Ω. Find the potential gradient along the wire.
14.
15.
16.
17. State two application of ultraviolet radiation.
18.
19. A parallel plate is charged by a battery. When the battery remains connected, a dielectric slab is
inserted in the space between the plate. Explain what changes if any, occur in the values of
(i) Potential difference between the plates
(ii) Electric field strength between the plates
(iii)Capacitance
(iv) Charge on the plate
(v) Energy stored in the capacitor?
20. Three points charges of +2𝜋𝐶, -3𝜋𝐶 are kept at the vertices A, B and C respectively of an equilateral
triangle of side 20 cm as shown in figure. What should be the sign and magnitude of charge to be
placed at the need point M of side BC so that charge at A remains in equilibrium ?
21. State Kirchhoff’s rules. Use these rules to write the expressions for the currents l1, l2 and l3 in the
circuit diagram shown.
22. Define the term electrical resistivity of material. Write its SI units. Derive an expression for the
resistivity of material in terms of number density and mass of free electrons present in it.
23.
24.
25.
26.
27. .Renu,Ritu and Kajal lived in a resettlement colony where they observed most houses stole
power from transmission lines using hooks. They had learnt in school about fire caused due to
electric short circuit. They decided to make people aware of the risks involved and also the
importance of paying their electricity bills. They got all their friends and responsible elders together
and with the help of the electricity board, succeeded in changing the situation.
b) A low voltage supply from which one needs high currents must have a very low internal
resistance, why?
c) A high tension supply of say 6 KV must have a very large internal resistance. Why?
28. i) Using Gauss’s theorem derive the expression for the electric field intensity at a point outside a
uniformly charged thin spherical shell of radius ‘R’ and surface charge density 𝜎C/m2.
Ii) Use Gauss’s theorem to find the value of electric field intensity at a point inside this shell ( or
hollow charged conducting sphere) ?
OR
Use Gauss’s law to obtain an expression for the electric field due to an infinitely long straight
uniformly charged wire.
Electric field in the above figure is directed along + X direction and given by Ex = 5Ax + 2B, where E
is in NC-1 and x is in metre, A and B are constants with dimensions Talking
and
-1
B = 5NC calculate.
(i) The electric flux through the cube. (ii)Net charge enclosed within the cube.
29. . (a) Draw the labelled diagram of moving coil galvanometer. Prove that in a radial magnetic field,
the deflection of the coil is directly proportional to the current flowing in the coil.
(b) A galvanometer can be converted into a voltmeter to measure up to (i) ‘V’ volts by connecting
a resistance R1 in series with coil. (ii)
volts by connecting a resistance R2 in series with its
coil. Find the resistance (R), in terms of R1 and R2 required to convert it into a voltmeter that
can read up to ‘2V’ volts.
OR
( a) Draw diagrams to depict the behaviour of magnetic field lines near a ‘ bar’ of :
(i) copper
(ii) Aluminium
(iii) Mercury, cooled to a very low temperature (4.2K )
(b) The vertical component of the earth’s agnetic field at a given place in
times its
horizontal component. If total intensity of earth’s magnetic field at the place is 0.4 G find the
value of :
(i) angle of dip
(ii) the horizontal component of earth’s magnetic field.
5
30.
XII – PHYSICS
SET NO-03
Time : 3 Hours
Marks : 70
Max.
1.Compare the electric flux in a cubical surface of side 10 cm and a spherical surface of radius 10
cm, when a change of 5μC is enclosed by them.
2. Two identical metal plates are given positive charges Q1 and Q2, where Q1 > Q2. Find the
potential difference between them, if they are now brought together to form a parallel plate capacitor
with capacitance C.
3. Can the terminal potential difference of a cell exceed its emf? Give reason for your answer.
4. Two wires of equal length one of copper and the other of manganin have the same resistance.
Which wire is thicker?
5. It is found that 1020 electrons pass from point X towards another point Y in 0.1s. How much is
the current & what is its direction?
6.The horizontal component of earth’s magnetic field is 0.2 G and total magnetic field is 0.4 G. Find
the angle of Dip.
7. How would you establish an instantaneous displacement current of 1A in the space between the
parallel plates of 1μF capacitor?
8. EMW travel in a medium at a speed of 2x108 m/s. the relative permeability of the medium is 1.0.
Calculate the relative permittivity?
9. Draw equipotential surfaces corresponding to a) a constant electric field in Z direction.
b) a field that uniformly increases in magnitude but remains in a constant (say Z) direction.
10. Define electric flux. Write its S.I unit. A charge q is enclosed by a spherical surface of radius R.
If the radius is reduced to half, how would the electric flux through the surface change ?
11. Is it possible that the terminal potential difference across the cell be zero ? If yes, state the
condition.
12. Derive an expression for the current density of a conductor in terms of the drift speed of electrons.
13. Draw the graphs showing variation of resistivity with temperature for
(i) Nichrome
(ii) silicon
14.
15.
16.
17. State two application of X-rays.
18. List any three properties of EM waves.
19.
20.
21. A potential difference of V volt is applied to a conductor of length L, and diameter D. How will
the drift velocity of electrons and the resistance of the conductor change when:
(i) V is doubled
(ii) L is halved and
(iii) D is halved, where in each case, the other two factors remain same. Give reason in each case.
22. In the circuit shown, R1 = 4Ω, R2= R3=5 Ω, R4= 10 Ω and E= 6V. Work out the equivalent
resistance of the circuit and the current in each resistor.
23. A Galvanometer of resistance 3663 ohm gives full scale deflection for a certain current Ig.
Calculate the value of the resistance of the shunt which when joined to the galvanometer coil will
result in 1/34 of the total current passing through the galvanometer. Also find the total resistance of
the Galvanometer and shunt.
24. Distingush between dia and ferro magnetic substance in respect of (i) Intensity of magnetisation.
(ii) Behaviour in an non uniform magnetic field. (iii) Suscetibility.
25.
26.
27. .Renu,Ritu and Kajal lived in a resettlement colony where they observed most houses stole
power
from transmission lines using hooks. They had learnt in school about fire caused due to electric short
circuit. They decided to make people aware of the risks involved and also the importance of paying
their
electricity bills. They got all their friends and responsible elders together and with the help of the
electricity board, succeeded in changing the situation.
• What values did Renu, Ritu and Kajal have?
• A low voltage supply from which one needs high currents must have a very low internal
resistance, why?
• A high tension supply of say 6 KV must have a very large internal resistance. Why?
28. Apply Gauss theorem to obtain the expression for the electric fielda) At a point due to an infinitely long, thin, uniformly charged straight wire of linear charge density
⋋cm-1
b) Near an infinite plane sheet of charge.
OR
Define electric potential at a point. Derive an expression for the electric potential at a point due to (a)
a point charge (b) a system of point charges (c) a dipole.
29. Two circular coils X and Y having radii R and R/2 respectively are placed in horizontal plane
with their centres coinciding with each other. Coil X has a current I flowing through it in the
clockwise sense. What must be the current in coil Y to make the total magnetic field at the common
centre of the two coils, zero?
With the same currents flowing in the two coils, if the coil Y is now lifted vertically upwards
through a distance R, what would be the net magnetic field at the centre of coil Y?
OR
A straight thick long wire of uniform cross section of radius ‘a’ is carrying a steady current I. Use
Ampere’s circuital law to obtain a relation showing the variation of the magnetic field (Br) inside
and outside the wire with distance r, ( r≤ 𝑎) and (r >a) of the field point from the centre of its cross
section. Plot a graph showing the nature of this variation.
Calculate the ratio of magnetic field at a point a/2 above the surface of the wire to that at a point a/2
below its surface. What is the maximum value of the field of this wire?
30.
XII – PHYSICS
SET NO-04
Time : 3 Hours
Max. Marks : 70
1. Two electric lines never cross each other. Why?
2..What is meant by electrostatic shielding?
3.Two square metal plates A and B are of the same thickness and material. The side of B is twice
that of side o fA. If the resistance of A and B are denoted by RA and RB, find RA/ RB.
4. If 6.25 × 1018 electrons flow through a given cross section in unit time, find the current.
5. An electric iron of resistance 80 Ω is operated at 200 V for two hours. Find the electrical energy
consumed.
6. An iron bar magnet is heated to 10000C and then cooled in a magnetic field free space. Will it
retain its magnetism?
7. What physical quantity is same for X-rays of wavelength 10-10 m, red light of wavelength 6800 Å
and radio wave of wavelength 500 m?
8. What is the effect of EMW on charged particles?
9. Two insulated charged copper spheres A and B of identical size have charges qA and qM respectively
A third sphere C of the same size but uncharged is brought in contact with the first and then in
contact with the second and finally removed from both. What are the new charges on A and B ?
10. Consider two conducting spheres of radii R1, and R2 with R1 > R2. If the two are at the same potential,
the larger sphere has more charge than the smaller sphere. State whether the charge density of the
smaller sphere is more or less than that of the larger one.
11.
What is the emf of a cell? On what factors does it depend?
12. Two cells, of emf and 2E and E, and internal resistances 2r and r respectively, are connected in
parallel. Obtain the expression for the equivalent emf and the internal resistance of the
combination.
13. In the meter bridge experiment, balance point was observed at J with AJ=l. a) The values of R
and X were doubled and then interchanged. What would be the new position of balance point ?
b) If the galvanometer and battery are intercharged at the balanced position, how will the
balance point get affected ?
14.
15.
16.
17. A parallel plate capacitor made of circular plates each of radius 10 cm has a capacitance 200pF.
The capacitor is connected to a 200V a.c. supply with an angular frequency of 200 rad/s.
a) What is the rms value of conduction current
b) Is the conduction current equal to displacement current
c) Peak value of displacement current
d) Determine the amplitude of magnetic field at a point 2cm from the axis between the plates
18.
19.
20.
21. State Kirchhoff’s rules of current distribution in an electrical network. Using these rules determine
the value of the current l1 in the electric circuit given below.
22. Derive the relation connecting drift speed of electrons and the electric current. Hence prove that
current density is directly proportional to the relaxation time.
23. A charged particle of mass ‘m’ charge ‘q’ moving at a uniform velocity ‘v’ enters a uniform
magnetic field ‘B’ normal to the field direction. Deduce an expression for Kinetic Energy of the
particle. Why does the Kinetic Energy of the charged particle not change when moving through the
magnetic field?
24. To increase the current sensitivity of a moving coil galvanometer by 50 % its resistance is increased
so that the new resistance becomes twice its initial resistance. By what factor does its voltage
sensitivity change?
25. Draw the phasor diagram showing voltage and current in LCR series circuit and derive an
expression for the impedance .
26. Two coils have a mutual inductance of 0.005H. The current changes in the first coil according to
the equation I= I0 Sin ωt where I0 =10A and ω=100Π rad/s. Calculate the maximum value of e.m.f
in the second coil.
27. The number of electrical generators used in areas where small workshops existed created lot of
pollution. Rishab and his five friends did a survey and realized that like in multistoried apartments, a
common generator could be set up for all these small workshops so that the noise and air pollution
could be reduced considerably. They had a tough time convincing the local bodies and now they are
going to the NGOs and some financiers to help them organize funds to do the needful. It is
admirable to see their perseverance.
a) What values did Rishab and his friends have?
b) Kamla pedals a stationary bicycle, the pedals of which are attached to a 100 turn coil of
area 0.10 sqmetres. The coil rotates at half a revolution per second and is placed in a
uniform magnetic field of 0.01 Tesla perpendiculars to the axis of rotation of the coil.
28. State Gauss’s theorem in electrostatics and express it mathematically. Using it derive an
expression for electric field at a point near a thin infinite plane sheet of electric charge. How does
this electric field change for a uniformly thick sheet of charge.
OR
What are dielectrics? Distinguish polar and nonpolar dielectrics. Define the term Polarization vector.
29.
30.
DESIGNED BY: MD. WASIM IQBAL ( HOD , PHYSICS FACULTY),
E- Mail id: [email protected], 7870647761
XII – PHYSICS
SET NO-05
Time : 3 Hours
Marks : 70
Max.
1. Why an electric dipole placed in a uniform electric field does not undergoes acceleration?
2. Why electric field lines (i) Cannot form closed loops sometimes? (ii) Cannot have break in between?
3. Which lamp has greater resistance (i) 60W and (ii) 100W when connected to the same supply?
4. Nichrome and Cu wires of the same length and same diameter are connected in series in an
electric circuit. In which wire will the heat be produced at a higher rate? Give reason.
5. An electric bulb rated for 500W at 100V is used in circuit having a 200V supply. Calculate the
resistance R that must be put in series with the bulb, so that the bulb delivers 500W.
6. Why permanent magnets are made of steel while the core of the transformer is made of soft iron?
7. The amplitude of of harmonic electromagnetic wave in vacuum is Bo=510 n T. What is the
amplitude of the electric field part of the wave?
8. The charging current for a capacitor is 0.25 A. what is the displacement current across its plates?
9.
10. How does the electric flux, electric field enclosing a given charge vary when the area enclosed
by the charge is doubled?
11.
What is the emf of a cell? On what factors does it depend?
12. Explain why an electric bulb becomes dim when an electric heater in parallel circuit is made on.
Why dimness decreases after some time?
13. A cell of emf ε and internal resistance r is connected across a variable resistor R. Plot a graph
showing the variation of terminal potential V with resistance R. Predict from the graph, the
condition under which V becomes equal to ε.
14. An α-particle moves with a speed of 5 × 105 𝑚 𝑠 −1 at an angle of 300 with respect to a magnetic
field of induction 10−4T. Find the force on the particle.
15.
16.
17.
18.
19.
20.
21. State Kirchhoff’s rules. Apply Kirchhoff’s rules to the loops ACBPA and ACBQA to write the
expression for the currents l1, l2, and l3 in the network.
22. On what principle a meter bridge work ? Draw a circuit diagram and explain how this device can
be used for determination of an unknown resistance.
23.
24.
25.
What do you mean by resonance in Series LCR circuit? Derive an expression for the frequency of
resonance in LCR circuit.
26. A 100 Ω resister is connected to 220V, 50 cycles per seconds. What is (i) peak potential difference
(ii) average potential difference and (iii) rms current?
28. Two capacitors with capacitances C1 and C2 are charged to potentials V1 and V2 respectively and
then connected in parallel. Calculate the common potential across the combination, the charge on
each capacitor, the electrostatic energy stored in the system and the change in electrostatic energy
from its initial value.
OR
29.a) State the principle of the working of a moving coil galvanometer,giving its labelled diagram.
b) "Increasing the current sensitivity of a galvanometer may not necessarily increase its voltage
sensitivity." Justify this statement.
(c) Outline the necessary steps to convert a galvanometer into an ammeter.
OR
30. a) Describe the principle construction theory and working of a transformer.
b) Describe the various losses in a transformer and explain how the losses can be minimized.
c) Show that the average value of AC over a complete cycle is zero.
OR
a) Show that the current and voltage are in phase in an ac circuit containing resistance only.
b)Deduce the phase relationship between current and voltage in an ac circuit containing inductor
only.
c) Define RMS value of AC and derive an expression for it.
XII – PHYSICS
SET NO-06
Time : 3 Hours
Marks : 70
Max.
1. A point charge Q is placed at point O as show in the figure is the potential difference
VA - VB positive, negative or zero, if Q is (i) POSITIVE (ii) NEGATIVE.
2.
3.
4.
5.
6.
7.
8.
Define electric dipole moment. Write its S.I unit
An incandescent lamp is operated at 240 V and the current is 0.5 A. What is the resistance
of the lamp ?
If the resistance of a coil is 2 Ω at 0oc and α = 0.004 /oC, then ,What is its resistance at
100o C.
In the case of insulators, as the temperature decreases, What happens to its resistivity.
A variable frequency a.c source is connected to a capacitor. Will the displacement current
How does a charge q oscillating at certain frequency produce electromagnetic wave?
9.
The electric field in a certain region of space is E = 104 𝑖 𝑁/𝐶 . How much is the flux passing
through an area ‘A’ if it is a part of XY plane, XZ plane, YZ plane, making an angle 30° with
the axis?
An electric dipole ±4μC is kept at co-ordinate points (1, 0, 4) are kept at (2,-1, 5), the electric
field is given by E= 20 i NC-1. Calculate the torque on the dipole.
11.
In a potentiometer arrangement, a cell of emf 1.25V give a balance point at 35cm length
of wire. If the cell is replaced by another cell and the balance point shifts to 63cm. what is
the emf of the second cell ?
12.Three cells of emf E, 2E and 5 E having internal resistances r, 2r and 3r, variable resistance R is
shown in the figure. Find the expression for the current. Plot a graph for variation of current with
R.
10.
13. Plot a graph showing the variation of terminal potential difference across a cell of emf ∈ and
internal resistance r with current drawn from it. Using this graph, how does one determine the
emf of the cell?
14. What is the value of magnetic moment of an electron revolving in the nth orbit of the H atom?
Also give the value of the Bohr magneton?
15. A circular coil of 200 turns, radius 5 cm carries a current of 2.5 A. It is suspended vertically in a
uniform horizontal magnetic field of 0.25 T, with the plane of the coil making an angle of 600 with
the field lines. Calculate the magnitude of the torque that must be applied on it to prevent it from
turning.
16.
17.
18.
19.
20.
21. Calculate the value of the resistance R in the circuit shown in the figure so that the current in the
circuit is 0.2 A. What would be the potential difference between points A and B.
22. Define resistivity of a conductor. Plot a graph showing the variation of resistivity with temperature
for a metallic conductor. How does one explain such a behavior, using the mathematical expression
of the resistivity of a material.
23.
24.
25. A rectangular coil of N turns and area of cross section A is held in a magnetic field B= B0 Sinωt
with the plane of the coil normal to B Deduce an expression for the e.m.f induced in the circuit.
26. In an LCR circuit the potential difference between terminals of inductance 60V, between terminals
of capacitor 40V and between the terminals of resistor is 40V. Find the supply voltage.
28. Derive the expression for the electric potential due to an electric dipole. Mention the contrasting
features of electric potential of a dipole at a point as compared to that due to a single charge.
OR
29.
OR
30. An A.C source of voltage V= Vm Sinωt is connected one-by-one to three circuit elements
X, Y and Z. It is observed that the current flowing in them
i)
is in phase with applied voltage for X
ii)
Lags applied voltage in phase by π /2 for elements Y.
iii)
Leads the applied voltage in phase by π /2 for element Z.
Identify the three circuit elements.
Find the expression for a) current flowing in the circuit b) net impedance of the circuit when the
same A.C source is connected across a series combination of the elements X, Y and Z.
If the frequency of the applied voltage is varied, set up in the condition of frequency when the current
amplitude in the circuit is maximum. Write the expression for current amplitude.
OR
Describe the mechanism of electromagnetic oscillations in LC circuit and write expression for the
frequency of oscillations produced.
XII – PHYSICS
SET NO-07
Time : 3 Hours
Max. Marks : 70
1. Two dipoles, made from charges ±q and ±Q respectively have equal dipole moments. Find the
ratio between the separations of these two pairs of charges.
2.
Name the Physical quantity whose S.I unit is JC-1. Is it a scalar or vector quantity ?
3.
4.
5.
6.
7. Give reason for decrease or increase in velocity of light, when it moves from air to glass or
glass to air respectively?
8.
9. Show that at a point where the electric field intensity is zero, electric potential need not be
zero.
10. A thin straight infinitely long conducting wire having charge density lambda is enclosed by
a cylindrical surface of radius r and length l, its axis coinciding with the length of the wire.
Find the expression for electric flux through the surface of the cylinder.
11. Plot a graph showing the variation of conductivity with the temperature in a metallic
conductor.
12. A copper wire is stretched to make it 0.2% longer. What is the percentage change in its
resistance?
13. A battery has an emf E and internal resistance r. A variable resistance R is connected across
the terminals of the battery. Find the value of R such that (a) the current in the circuit is maximum (b)
the potential difference across the terminal is maximum.
14. Calculate the torque acting on a magnet of length 20 cm and pole strength 2 x 10 -5 Am, placed in
the earth’s magnetic field of flux density 2 x 10 -5 T, when (a) magnet is parallel to the field (b) magnet
is perpendicular to the field.
15. The susceptibility of a magnetic material is 0.9853. Identify the type of the magnetic material.
Draw the modification of the field pattern on keeping a piece of this material in a uniform magnetic
field.
16.
17.
18.
19.
20.
21. Write the mathematical relation for the resistivity of a material in terms of relaxation time, number
density and mass and charge of charge carriers in it. Explain, using this relation, why the resistivity
of a metal increases and that of a semiconductor decreases with rise in temperature.
22. State Kirchhoff’s rules. Apply these rules to the loops PRSP and PRQP to write the expressions
for the currents l1, l2 and l3 in given circuit.
23.
24.
25. Define quality factor (Q factor) of resonance and derive an expression for it.
26. Two coils have a mutual inductance of 0.005H. The current changes in the first coil according to
the equation I= I0 Sin ωt where I0 =10A and ω=100Π rad/s. Calculate the maximum value of e.m.f in
the second coil.
OR
OR
i)
ii)
iii)
OR
XII – PHYSICS
SET NO-08
Time : 3 Hours
Max. Marks : 70
1. If a point charge +q is taken from A to C and then from C to B of a circle drawn with another point
charge q at its centre, then along which path will more work be done
2. Sketch a graph to show how the charge Q acquired by a capacitor of capacitance
C raises with increase in Potential difference between its plates.
Q.N: 3,4 &5 as below:
6.
7. The charging current for a capacitor is 0.25 A. what is the displacement current across its plates?
8. What is the effect of EMW on charged particles?
9. Two electric charges 3μC, -4μC are placed at the two corners of an isosceles right angled triangle
of side 1 m as shown in the figure. What is the direction and magnitude of electric field at A due to
the two charges?
10.Two identical metal plates are given positive charges Q1 and Q2, where Q1 > Q2. Find the potential
difference between them, if they are now brought together to form a parallel plate capacitor with
capacitance C.
11. A piece of silver wire has a resistance of 1Ω. What will be the resistance of the constantan wire of
one third of its length and one half of its diameter if the specific resistance of the constantan wire is
30 times than that of the silver?
12. Two cells each of emf E and internal resistances r1 and r2 are connected in series to an external
resistance R. Can a value of R be selected such that the potential difference of the first cell is 0.
13.
14. A long straight solid metal wire of radius ‘R’ carries a current ‘I’, uniformly distributed over its
circular cross section. Find the magnetic field at a distance ‘r’ from the axis of the wire (a) inside and
(b) outside the wire .
15. A long straight conductor PQ , carrying a current of 60 A, is fixed horizontally. Another long
conductor XY is kept parallel to PQ at a distance of 4 mm, in air. Conductor XY is free to move and
carries a current ‘I’ . Calculate the magnitude and direction of current ‘I’ for which the magnetic
repulsion just balances the weight of the conductor XY.
16.
17.
18. List three properties of EM waves.
19.
20.
21. A cell of unknown emf ε and internal resistance r, two unknown resistances R1, and R2 and
R2(R2>R1) and a perfect ammeter are given. The current in the circuit is measured in five different
situations.
(a) Without any external resistance in the circuit,
(b) With resistance R1 only,
(c) With resistance R2 only,
(d) With both R1 and R2 used in series combination,
(e) With both R1 and R2 used in parallel combination.
The current obtained in the five cases are 0.42A, but not necessarily in that order. Identify the
currents in the five cases listed above and calculate ε, r, R1 and R2.
22. A conductor of length l is connected to a d.c. source of potential V. If the length of the conductor
is tripled by stretching it, keeping V constant, explain how do the following factors vary in the
conductor.
i) Drift speed of electrons
ii) Resistance
iii) Resistivity
23.
24.
25.
26. Derive an expression for the average power in an ac circuit.
27.Renu,Ritu and Kajal lived in a resettlement colony where they observed most houses stole power
from transmission lines using hooks. They had learnt in school about fire caused due to electric short
circuit. They decided to make people aware of the risks involved and also the importance of paying
their electricity bills. They got all their friends and responsible elders together and with the help of
the electricity board, succeeded in changing the situation.
b)A low voltage supply from which one needs high currents must have a very low internal
resistance, why?
c)A high tension supply of say 6 KV must have a very large internal resistance. Why?
28. Derive an expression for the energy stored in a capacitor. Show that whenever two conductors
share charges by bringing them into electrical contact, there is a loss of energy.
OR
29.
OR
30.
XII – PHYSICS
SET NO-09
Time : 3 Hours
Marks : 70
Max.
1. In which Orientation, a dipole placed in uniform electric field is in (a) stable (b) unstable
equilibrium.
2. Two point charges having equal charges separated by 1 mt. in distance experience a force of 8 N.
What will be the force experienced by them, If they are held in water, at the same distance.
(dielectric constant of water = 80).
Q.NO: 3,4 & 5respectively as below:
6.
7. If E and B represent electric and magnetic field vectors of the electromagnetic waves, then what is
the direction of propagation of the electromagnetic wave?
8. Calculate the wavelength of EMW emitted by the oscillator antenna system, if L= 0.253 μH & C =
25Pf ?
9. 27 small drops of mercury having the same radius collapse to form one big drop. Find the ratio of
the capacitance of the big drop to small drop.
10. A uniformly charged rod with linear charge density λ of length L is inserted into a hollow cubical
structure of side ’L’ with constant velocity and moves out from the opposite face. Draw the graph
between flux and time.
11.
12.
14. An electron moving with Kinetic Energy 25 keV moves perpendicular to a uniform magnetic
field of 0.2 mT. Calculate the time period of rotation of electron in the magnetic field.
15. A proton, alpha particle and deuteron are moving in circular paths with same kinetic energies in
the same magnetic fields. Find the ratio of their radii and time periods.
16.
17. Write any two application of X-rays.
18.
19.
20.
21. In the figure, a long uniform potentiometer wire AB is having a constant potential gradient along
its length. The null points for the two primary cells of emf E1 and E2 connected in the manner
shown, are obtained at a distance of 120 cm and 300 cm from the end A. Find (a) E 1/E2 and (b)
position of null point for the cell E1. How is the sensitivity of a potentiometer increased ?
22. The circuit shown in the diagram contains a battery B, a
rheostat Rh and identical lamps P and Q. What will happen to the brightness of the lamps, if the
resistance through the rheostat is increased? Give reasons.
23.
24.
25.
26. Define power factor. Deduce expression for it and explain wattless current?
admirable to
see their perseverance.
i) What values did Rishab and his friends have?
ii)Kamla pedals a stationary bicycle, the pedals of which are attached to a 100 turn coil of
What is the maximum voltage generated in the coil?
28.
OR
29.
30.
XII – PHYSICS
SET NO-10
Time : 3 Hours
Marks : 70
1.
Max.
A point charge Q is placed at point O as show in the figure is the potential difference
VA - VB positive, negative or zero, if Q is (i) POSITIVE (ii) NEGATIVE.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Define electric dipole moment. Write its S.I unit
An incandescent lamp is operated at 240 V and the current is 0.5 A. What is the resistance
of the lamp ?
If the resistance of a coil is 2 Ω at 0oc and α = 0.004 /oC, then ,What is its resistance at
100o C.
In the case of insulators, as the temperature decreases, What happens to its resistivity.
A variable frequency a.c source is connected to a capacitor. Will the displacement current
How does a charge q oscillating at certain frequency produce electromagnetic wave?
9. Two electric charges 3μC, -4μC are placed at the two corners of an isosceles right angled
triangle of side 1 m as shown in the figure. What is the direction and magnitude of electric
field at A due to the two charges?
10.Two identical metal plates are given positive charges Q1 and Q2, where Q1 > Q2. Find
the potential difference between them, if they are now brought together to form a parallel
plate capacitor with capacitance C.
11. A piece of silver wire has a resistance of 1Ω. What will be the resistance of the constantan
wire of one third of its length and one half of its diameter if the specific resistance of the
constantan wire is 30 times than that of the silver?
12. Two cells each of emf E and internal resistances r1 and r2 are connected in series to an
external resistance R. Can a value of R be selected such that the potential difference of the
first cell is 0.
13.
13.
14.
14. A long straight solid metal wire of radius ‘R’ carries a current ‘I’, uniformly distributed
over its circular cross section. Find the magnetic field at a distance ‘r’ from the axis of the
wire (a) inside and (b) outside the wire .
15. A long straight conductor PQ , carrying a current of 60 A, is fixed horizontally. Another
long conductor XY is kept parallel to PQ at a distance of 4 mm, in air. Conductor XY is free
to move and carries a current ‘I’ . Calculate the magnitude and direction of current ‘I’ for
which the magnetic repulsion just balances the weight of the conductor XY.
15.
16.
17.
18. List three properties of EM waves.
19.
20.
shown, are obtained at a distance of 120 cm and 300 cm from the end A. Find (a) E1/E2 and (b)
23.
24.
25.
admirable to
• What values did Rishab and his friends have?
• Kamla pedals a stationary bicycle, the pedals of which are attached to a 100 turn coil of
20.
shown, are obtained at a distance of 120 cm and 300 cm from the end A. Find (a) E1/E2 and (b)
23.
24.
25.
admirable to
• What values did Rishab and his friends have?
• Kamla pedals a stationary bicycle, the pedals of which are attached to a 100 turn coil of
OR
OR
i)
ii)
iii)
OR

XII - Govind Vidyalaya

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