CBSE Class 12 Physics Alternating Current MCQs
Q.1 The power factor in a circuit connected to an A.C. The value of power factor is
Options:
(a) unity when the circuit contains an ideal inductance only
(b) unity when the circuit contains an ideal resistance only
(c) zero when the circuit contains an ideal resistance only
(d) unity when the circuit contains an ideal capacitance only
Answer=B
Q.2 In series combination of R, L and C with an A.C. source at resonance, if R = 20 ohm, then impedence Z of the combination is
Options:
(a) 20 ohm (b) zero (c) 10 ohm (d) 400 ohm
Answer=A
Q.3 In an LCR series a.c. circuit, the voltage across each of the components, L, C and R is 50V. The voltage across the LC combination will be
Options:
(a) 100 V (b) 150 V
(c) 50 V (d) 0 V
Answer=D
Q.4 Choose the correct option
Assertion : When the frequency of the AC source in an LCR circuit equals the resonant frequency, the reactance of the circuit is zero, and so there is no current through the inductor or the capacitor.
Reason : The net current in the inductor and capacitor is zero.
Options:
(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct
Answer=D
Q.5 A coil of 40 henry inductance is connected in series with a resistance of 8 ohm and the combination is joined to the terminals of a 2 volt battery. The time constant of the circuit is
Options:
(a) 20 seconds (b) 5 seconds
(c) 1/5 seconds (d) 40 seconds
Answer=B
Q.6 A current of 4A flows in a coil when connected to a 12V dc source. If the same coil is connected to a 12V, 50 rad/s a.c. source, a current of 2.4A flows in the circuit. Determine the inductance of the coil.
Options:
(a) 0.08 H (b) 0.04 H (c) 0.02 H (d) 1 H
Answer=A
Q.7 An inductive circuit contains resistance of 10 ohms and an inductance of 2 henry. If an A.C. voltage of 120 Volts and frequency 60 Hz is applied to this circuit, the current would be nearly
Options:
(a) 0.32 A (b) 0.16 A (c) 0.48 A (d) 0.80 A
Answer=B
Q.8 A transformer is employed to
Options:
(a) convert A.C. into D.C.
(b) convert D.C. into A.C.
(c) obtain a suitable A.C. voltage
(d) obtain a suitable D.C. voltage
Answer=C
Q.9 The transformer voltage induced in the secondary coil of a transformer is mainly due to
Options:
(a) a varying electric field
(b) a varying magnetic field
(c) the vibrations of the primary coil
(d) the iron core of the transformer
Answer=B
Q.10 The loss of energy in the form of heat in the iron core of a transformer is
Options:
(a) iron loss (b) copper loss
(c) mechanical loss (d) None of these
Answer=A
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