# CBSE Class 12 Physics Alternating Current MCQs

## MCQ for Class 12 Physics Alternating Current

Class 12 Physics students should refer to the following multiple-choice questions with answers for Alternating Current in standard 12. These MCQ questions with answers for Grade 12 Physics will come in exams and help you to score good marks

### Alternating Current MCQ Questions Class 12 Physics with Answers

Question: Alternating current cannot be measured by D.C. ammeter, because

(a) A. C. is virtual
(b) A. C. changes its direction
(c) A. C. cannot pass through D.C. ammeter
(d) average value of A. C for complete cycle is zero

Question: A.C. power is transmitted from a power house at a high voltage as

(a) the rate of transmission is faster at high voltages
(b) it is more economical due to less power loss
(c) power cannot be transmitted at low voltages
(d) a precaution against theft of transmission lines

Question: If the frequency of an A.C. is made 4 times of its initial value, the inductive reactance will
(a) be 4 times
(b) be 2 times
(c) be half
(d) remain the same

Question: When an ac voltage of 220 V is applied to the capacitor C, then
(a) the maximum voltage between plates is 220 V.
(b) the current is in phase with the applied voltage.
(c) the charge on the plate is not in phase with the applied votage.
(d) power delivered to the capacitor per cycle is zero

Question: An A.C. source is connected to a resistive circuit. Which of the following is true?
(b) Current lags behind voltage in phase
(c) Current and voltage are in same phase
(d) Any of the above may be true depending upon the value of resistance.

Question: With increase in frequency of an A.C. supply, the inductive reactance
(a) decreases
(b) increases directly with frequency
(c) increases as square of frequency
(d) decreases inversely with frequency

Question: The capacitive reactance in an A.C. circuit is
(a) effective resistance due to capacity
(b) effective wattage
(c) effective voltage
(d) None of these

Question: In which of the following circuits the maximum power dissipation is observed?
(a) Pure capacitive circuit
(b) Pure inductive circuit
(c) Pure resistive circuit
(d) None of these

Question: In an L.C.R. series a.c. circuit, the current
(a) is always in phase with the voltage
(b) always lags the generator voltage
(c) always leads the generator voltage
(d) None of these

Question: If an LCR series circuit is connected to an ac source, then at resonance the voltage across
(a) R is zero
(b) R equals the applied voltage
(c) C is zero
(d) L equals the applied voltage

Question: In general in an alternating current circuit
(a) the average value of current is zero
(b) the average value of square of the current is zero
(c) average power dissipation is zero
(d) the phase difference between voltage and current is zero

Question: The frequency of A.C. mains in India is
(a) 30 c/s
(b) 50 c/s
(c) 60 c/s
(d) 120 c/s

Question: A.C. power is transmitted from a power house at a high voltage as
(a) the rate of transmission is faster at high voltages
(b) it is more economical due to less power loss
(c) power cannot be transmitted at low voltages
(d) a precaution against theft of transmission lines

Question: The electric mains supply in our homes and offices is a voltage that varies like a sine function with time such a voltage is called ... A... and the current driven by it in a circuit is called the ... B... Here, A and B refer to
(a) DC voltage, AC current
(b) AC voltage, DC current
(c) AC voltage, DC voltage
(d) AC voltage, AC current

Question: Alternating currents can be produced by a
(a) dynamo
(b) choke coil
(c) transformer
(d) electric motor

Question: The alternating current of equivalent value of I0√2 is
(a) peak current
(b) r.m.s. current
(c) D.C. current
(d) all of these

Question: The parallel combination of inductor and capacitor is called as
(a) rectifier circuit
(b) tank circuit
(c) acceptor circuit
(d) filter circuit

Question: The peak value of the a.c. current flowing throw a resistor is given by
(a) I0 = e0/R
(b) I = e/R
(c) I0 = e0
(d) I0 = R/e0

Question: The alternating current can be measured with the help of
(a) hot wire ammeter
(b) hot wire voltmeter
(c) moving magnet galvanometer
(d) suspended coil type galvanometer

Question: Alternating current can not be measured by D.C. ammeter, because
(a) A. C. is virtual
(b) A. C. changes its direction
(c) A. C. can not pass through D.C. ammeter
(d) average value of A. C for complete cycle is zero

Question: The core of transformer is laminated to reduce
(a) flux leakage
(b) hysteresis
(c) copper loss
(d) eddy current

Question: A transformer is based on the principle of
(a) mutual induction
(b) self induction
(c) Ampere’s law
(d) X-ray crystallography

Question: The transformation ratio in the step-up transformer is
(a) one
(b) greater than one
(c) less than one
(d) the ratio greater or less than one depends on the other factor

Question: An A.C. source is connected to a resistive circuit. Which of the following is true?
(b) Current lags behind voltage in phase
(c) Current and voltage are in same phase
(d) Any of the above may be true depending upon the value of resistance.

Question: With increase in frequency of an A.C. supply, the inductive reactance
(a) decreases
(b) increases directly with frequency
(c) increases as square of frequency
(d) decreases inversely with frequency

Question: The average power dissipated in a pure inductance is
(a) 1/2LI2
(b) LI2
(c) LI2 / 4
(d) zero

Question: In the case of an inductor
(a) voltage lags the current by Π/2
(b) voltage leads the current by Π/2
(c) voltage leads the current by  Π/3
(d) voltage leads the current by Π/4

Question: Eddy currents in the core of transformer can't be developed by
(a) increasing the number of turns in secondary coil
(b) taking laminated transformer
(c) making step down transformer
(d) using a weak a.c. at high potential

Question: Quantity that remains unchanged in a transformer is
(a) voltage
(b) current
(c) frequency
(d) None of these

Question: If the frequency of an A.C. is made 4 times of its initial value, the inductive reactance will
(a) be 4 times
(b) be 2 times
(c) be half
(d) remain the same

Question: An inductance L having a resistance R is connected to an alternating source of angular frequency ω The Quality factor Q of inductance is
(a) R/ ωL
(b) (ωL/R)2
(c) (R /ωL)½
(d) ωL/R

Question: A capacitor acts as an infinite resistance for
(a) DC
(b) AC
(c) DC as well as AC
(d) neither AC nor DC

Question: The capacitive reactance in an A.C. circuit is
(a) effective resistance due to capacity
(b) effective wattage
(c) effective voltage
(d) None of these

Question: Of the following about capacitive reactance which is correct?
(a) The reactance of the capacitor is directly proportional to its ability to store charge
(b) Capacitive reactance is inversely proportional to the frequency of the current
(c) Capacitive reactance is measured in farad
(d) The reactance of a capacitor in an A.C. circuit is similar to the resistance of a capacitor in a D.C. circuit

Question: Phase difference between voltage and current in a capacitor in an ac circuit is
(a) π
(b) π/2
(c) 0
(d) π/3

Question: A capacitor has capacitance C and reactance X, if capacitance and frequency become double, then reactance will be
(a) 4X
(b) X/2
(c) X/4
(d) 2X

Question: When an ac voltage of 220 V is applied to the capacitor C, then
(a) the maximum voltage between plates is 220 V.
(b) the current is in phase with the applied voltage.
(c) the charge on the plate is not in phase with the applied votage.
(d) power delivered to the capacitor per cycle is zero.

Question: In LCR circuit if resistance increases quality factor
(a) increases finitely
(b) decreases finitely
(c) remains constant
(d) None of these

Question: An inductor, a resistor and a capacitor are joined in series with an AC source. As the frequency of the source is slightly increased from a very low value, the reactance of the
(a) inductor increases
(b) resistor increases
(c) capacitor increases
(d) circuit increases

Question: With increase in frequency of an A.C. supply, the impedance of an L-C-R series circuit
(a) remains constant
(b) increases
(c) decreases
(d) decreases at first, becomes minimum and then increases.

Question: If an LCR series circuit is connected to an ac source, then at resonance the voltage across
(a) R is zero
(b) R equals the applied voltage
(c) C is zero
(d) L equals the applied voltage

Question: The loss of energy in the form of heat in the iron core of a transformer is
(a) iron loss
(b) copper loss
(c) mechanical loss
(d) None of these

Question: In an L.C.R. series a.c. circuit, the current
(a) is always in phase with the voltage
(b) always lags the generator voltage
(c) always leads the generator voltage
(d) None of these

Question: An LCR series circuit, connected to a source E, is at resonance. Then the voltage across
(a) R is zero
(b) R equals applied voltage
(c) C is zero
(d) L equals applied voltage

Question: A transformer is employed to
(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

Question: Transformers are used
(a) in DC circuit only
(b) in AC circuits only
(c) in both DC and AC circuits
(d) neither in DC nor in AC circuits

Question: Power factor of the A. C. circuit varies between
(a) 0 to 0.5
(b) 0.5 to 1
(c) 0 to 1
(d) 1 to 2

Question: The graph between inductive reactance and frequency is
(a) parabola
(b) straight line
(c) hyperbola
(d) an arc of a circle

Question: For minimum dissipation of energy in the circuit the power factor should be
(a) large
(b) small
(c) moderate
(d) can not say

Question: The transformer voltage induced in the secondary coil of a transformer is mainly due to
(a) a varying electric field
(b) a varying magnetic field
(c) the vibrations of the primary coil
(d) the iron core of the transformer

Question: The power factor in a circuit connected to an A.C. The value of power factor is
(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

Question: 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
(a) 20 ohm
(b) zero
(c) 10 ohm
(d) 400 ohm

Question: 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
(a) 100 V
(b) 150 V
(c) 50 V
(d) 0 V

Question: 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.
(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

Question: 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

(a) 20 seconds
(b) 5 seconds
(c) 1/5 seconds
(d) 40 seconds

Question: 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.

(a) 0.08 H
(b) 0.04 H
(c) 0.02 H
(d) 1 H

Question: 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

(a) 0.32 A
(b) 0.16 A
(c) 0.48 A
(d) 0.80 A

Question: A transformer is employed to

(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

Question: The transformer voltage induced in the secondary coil of a transformer is mainly due to

(a) a varying electric field
(b) a varying magnetic field
(c) the vibrations of the primary coil
(d) the iron core of the transformer

Question:  The loss of energy in the form of heat in the iron core of a transformer is

(a) iron loss
(b) copper loss
(c) mechanical loss
(d) None of these

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