Electromagnetic induction 1. If the instantaneous current in a circuit

Prof. Yogesh Jahagirdar’s
Academy of Physics
Electromagnetic induction
1
1. If the instantaneous current in a circuit is given by i = 2 c os ( t +)
amperes, the r.m.s value of the current is
a) 2 A
b) 2 A
c) 22 A
d) Zero ampere
2. The instantaneous voltage across a pure capacitor
a) Leads current in phas e by /2
b) Lags behind the current in phase by /2
c) Is in phase with the current
d) Lags behind current in phase by an angle depending on frequency
3. An alternating current of frequency f is flowing in a circuit containing a
resistance R and choke L in series. The impedance of the circuit is equal to
a) R
b) R 2  4π 2f 2L2
c) R + 2 f L d) R/2  f L
4. An A.C source is connected to a resistive circuit.
W hat is true of the following?
a) Current leads ahead of voltage in phase
b) Current lags behind v oltage in phase
c) Current and voltage are in the same phase
d) Any of the above may be true depending upon the value of resistance
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Prof. Yogesh Jahagirdar’s
Academy of Physics
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5. An inductive circuit has zero resistance when D.C voltage is applied, the current lags
behind the voltage by
a) 30 0
b) 45 0
c) 90 0
d) 0 0
6. A generator produces a voltage given by V = 240 sin 120t volt where t is in seconds.
The frequency and r.m.s voltage is
a) 60Hz and 240 V
b) 19Hz and 120 V
c) 19Hz and 170V
d) 754Hz and 170V
7. Same current is flowing in two A.C circuits. The first contains only inductance and
second contains only capacitance. If the frequency of emf of AC is increased for both,
the effect on the current will be
a) Increases in first and decr eases in second
b) Increases in both
c) Decreases in both
d) Decreases in first circuit and increases in second
8. A 20V A.C is applied to a circuit consisting of a resistance and a coil with a
negligible resistanc e. If voltage across the resistanc e is 12 volt, the voltage
across the coil is
a) 16V
b) 10V
c) 8V
d) 6V
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Prof. Yogesh Jahagirdar’s
Academy of Physics
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9. The peak value of an A.C is E = E 0 sin t at 10V and its frequency is 50Hz.
At a time t =1/600s, the instantaneous value of emf is
a) 10V
b) 53 V
c) 5V
d) 1V
10. An A.C E = 200 2 sin 100t is connected to a microfarad capacitor through
an A.C ammeter. The reading of the ammeter is
a) 10 mA
b) 20 mA
c) 40 mA
d) 80 mA
11. An A.C source is of 200 /2V, 50 Hz the value of voltage after 1/600 s from
start is
a) 200 V
b) 200 /2 V
c) 100 V
d) 50 V
12. D.C ammeter is connected in a circuit through which A.C of 50Hz flows .
The ammeter would read
a) Peak value of current
b) Average current
c) Zero
d) R.M.S value of current
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Prof. Yogesh Jahagirdar’s
Academy of Physics
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13. A coi l having 225 tur ns, each of area 0.04 m 2 is rotated at constant rate of
180 revolutions per second in external magnetic field of induction 5T about
an axis lying in the plane of the coil and perpendicular to the external
magnetic field. The maximum induced e. m. f. in the c oil will be
a) 54kV
b) 96kV
c) 486V
d) 2400V
14. An alternating voltage given by e = 300 sin 376.99tV, is applied to a series
combination of an inductance and a c apacitance of reactance 100 and
200. The equation of current through the circuit is
a) i = 3 sin 376.99t A
b) i = 3 cos 376.99t A
c) i = - 3 cos376.99t A
d) i = 3 cos 376.99t + /2) A
15. The A. C. supply voltage of 200 V r.m .s and a frequency of 50 Hz, connected
to a series c ombination of resistance 200 and an inductance of 2/ H.
The equation of the current is
π
π
a) 2sin(100πi  )
b) i  2sin(100πs - )
4
4
π
π
c) i  1sin(100πs - )
d) i  1sin(100πs  )
4
4
16. The r eactance of a 0.1
a)1600, 154
c)1.6k, 1.5k
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f capacitor at 100 Hz and 105 Hz is
b)16k, 15k
d) 26k, 24k
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Prof. Yogesh Jahagirdar’s
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17. In the above problem, if 100 volt (r. m. s) signal applied at smaller
frequency, the peak value of the current at 100Hz will be
a) 6.25mA
b) 6.252mA
c) 6.25/2m
d) 6.252A
18. A pure resistance of 100 ohm is in series with a pure capacitance of 50 F.
The series c ombination is connected across 230V, 50 Hz supply.
The capacitive reactance
a) 60
b) 58k
c) 6.7
d) 48
19. In the above problem, the current will be
a) 2.43A
b)1.25A
c) 1.94A
d) 2.25A
20. In the problem no.24, the power factor will be
a) 0.65
b) 0.54
c) 0.35
d) 0.84
21. In the problem no. 24, the phase angle wi ll be
a) 45
b) 32
c) 27
d) 55
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Academy of Physics
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22. In the problem no. 24, voltage across resistor will be
a) 135V
b) 182V
c) 194V
d) 165V
23. In the problem no. 24, voltage across capacitor will be
a) 117.5V
b) 135.2V
c) 94.5V
d) 145.3V
24. A 50 volt 10 watt lamp is to be run on 200V 50 Hz mains. The inductance
of a choke required in the circuit will be
a) 2H
b)
3H
c) 4H
d)
5H
25. A current of 1mA (rms) is sent through a series combination of a resistance
of 1k , an inductance of 10 H and a capacitance of 1 F by an a. c.
source of frequency 50 Hz. The amplitude of the applied voltage wi ll be
a) 2V
b) 2V
c) 4V
d) 4V
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