# ac Circuit Questions and Answers

### ac Circuits (Physics) Problems / Answers:

Ques: Which of the following components of a LCR circuit, with ac supply, dissipates energy?
(a) L
(b) R
(c) C
(d) All of these

Ans. (b)

Ques. Current in the circuit is wattless, if
(a) Inductance in the circuit is zero
(b) Resistance in the circuit is zero
(c) Current is alternating
(d) Resistance and inductance both are zero

Ans. (b)

Ques. Radio frequency choke uses core of
(a) Air
(b) Iron
(c) Air and iron
(d) None of these

Ans. (a)

Ques: In a LCR circuit the pd between the terminals of the inductance is 60 V, between the terminals of the capacitor is 30V and that between the terminals of resistance is 40V. the supply voltage will be equal to â€¦â€¦
(a) 50 V
(b) 70 V
(c) 130 V
(d) 10 V

Ans. (a)

Ques: In an A.C. circuit the current
(b) Always lags behind the voltage
(c) Is always in phase with the voltage
(d) May lead or lag behind or be in phase with the voltage

Ans. (d)

Ques. A 120 volt ac source is connected across a pure inductor of inductance 0.70 henry. If the frequency of the source is 60 Hz, the current passing through the inductor is
(a) 4.55 amps
(b) 0.355 amps
(c) 0.455 amps
(d) 3.55 amps

Ans. (c)

Ques: In a ac circuit of capacitance the current from potential is
(a) Forward
(b) Backward
(c) Both are in the same phase
(d) None of these

Ans. (a)

Ques. For high frequency, a capacitor offers
(a) More reactance
(b) Less reactance
(c) Zero reactance
(d) Infinite reactance

Ans. (b)

Ques: The coil of choke in a circuit
(a) Increases the current
(b) Decreases the current
(c) Does not change the current
(d) Has high resistance to dc circuit

Ans. (b)

Ques: In an ac circuit, the power factor
(a) Is zero when the circuit contains an ideal resistance only
(b) Is unity when the circuit contains an ideal resistance only
(c) Is zero when the circuit contains an ideal inductance only
(d) Is unity when the circuit contains an ideal inductance only

Ans. (b)
(c)

Ques: A 0.7 henry inductor is connected across a 120V â€“ 60 Hz ac source. The current in the inductor will be very nearly
(a) 4.55 amp
(b) 0.355 amp
(c) 0.455 amp
(d) 3.55 amp

Ans. (c)

Ques. In an ac circuit, the potential difference across an inductance and resistance joined in series are respectively 16 V and 20 V. The total potential difference across the circuit is
(a) 20.0 V
(b) 25.6 V
(c) 31.9 V
(d) 53.5 V

Ans. (b)

Ques: The capacity of a pure capacitor is 1 farad. In dc circuits, its effective resistance will be
(a) Zero
(b) Infinite
(c) 1 ohm
(d) 1/2 ohm

Ans. (b)

Ques. Same current is flowing in two alternating circuits. The first circuit contains only inductance and the other contains only a capacitor. If the frequency of the e.m.f. of ac is increased, the effect on the value of the current will be
(a) Increases in the first circuit and decreases in the other
(b) Increases in both the circuits
(c) Decreases in both the circuits
(d) Decreases in the first circuit and increases in the other

Ans. (d)

Ques: What will be the phase difference between virtual voltage and virtual current, when the current in the circuit is wattles
(a) 90Â°
(b) 45Â°
(c) 180Â°
(d) 60Â°

Ans. (a)

Ques: In a purely resistive ac circuit, the current
(a) Lags behind the e.m.f. in phase
(b) Is in phase with the e.m.f.
(c) Leads the e.m.f. in phase
(d) Leads the e.m.f. in half the cycle and lags behind it in the other half

Ans. (b)

Ques: The reactance of a coil when used in the domestic ac power supply (220 volt, 50 cycles) is 100 ohm. The self inductance of the coil is nearly
(a) 3.2 henry
(b) 0.32 henry
(c) 2.2 henry
(d) 0.22 henry

Ans. (b)

Ques. The power factor of a good choke coil is
(a) Nearly zero
(b) Exactly zero
(c) Nearly one
(d) Exactly one

Ans. (a)

Ques: In LCR circuit, the capacitance is changed from C to 4C. For the same resonant frequency, the inductance should be changed from L to
(a) 2L
(b) L / 2
(c) L / 4
(d) 4 L

Ans. (c)

Related: mechanical wave MCQ

Ques: An alternating current source of frequency 100 Hz is joined to a combination of a resistance, a capacitance and a coil in series. The potential difference across the coil, the resistance and the capacitor is 46, 8 and 40 volt respectively. The electromotive force of alternating current source in volt is
(a) 94
(b) 14
(c) 10
(d) 76

Ans. (c)

Ques: In an ac circuit, a resistance of R ohm is connected in series with an inductance L. If phase angle between voltage and current be 45Â°, the value of inductive reactance will be
(a) R/4
(b) R/2
(c) R
(d) Cannot be found with the given data

Ans. (c)

Ques: An alternating voltage is connected in series with a resistance R and an inductance L If the potential drop across the resistance is 200 V and across the inductance is 150 V, then the applied voltage is
(a) 350 V
(b) 250 V
(c) 500 V
(d) 300 V

Ans. (b)

Ques: A 20 volts ac is applied to a circuit consisting of a resistance and a coil with negligible resistance. If the voltage across the resistance is 12 V, the voltage across the coil is
(a) 16 volts
(b) 10 volts
(c) 8 volts
(d) 6 volts

Ans. (a)

Related: Mensuration maths problems

Ques: A capacitor is a perfect insulator for
(a) Alternating currents
(b) Direct currents
(c) Both ac and dc
(d) None of these

Ans. (b)

Ques: A choke coil is preferred to a rheostat in ac circuit as
(a) It consumes almost zero power
(b) It increases current
(c) It increases power
(d) It increases voltage

Ans. (a)

Ques: A choke coil has
(a) High inductance and low resistance
(b) Low inductance and high resistance
(c) High inductance and high resistance
(d) Low inductance and low resistance

Ans. (a)

Ques. The impedance of a circuit consists of 3 ohm resistance and 4 ohm reactance. The power factor of the circuit is
(a) 0.4
(b) 0.6
(c) 0.8
(d) 1.0

Ans. (b)