NEET Physics AC Circuit LCR Circuit Quality and Power Factor MCQs Set A

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

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

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

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

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

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

Question: In a series resonant circuit, having L,C and R as its elements, the resonant current is i. The power dissipated in circuit at resonance is
a) i² R
b) zero
c) Both
d) None of these
Answer: i² R

Question: At resonant frequency the current amplitude in series LCR circuit is
a) maximum
b) zero
c) minimum
d) infinity
Answer: maximum

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 resistance only
b) zero when the circuit contains an ideal resistance only
c) unity when the circuit contains an ideal inductance only
d) unity when the circuit contains an ideal capacitance only
Answer: unity when the circuit contains an ideal resistance only

Question:

a)

b)

c)

d)

Answer:

Question: An A. C. of frequency f is flowing in a circuit containing a resistance R and capacitance C in series. The impedance of the circuit is equal to

a)

b)

c)

d) None of these

Answer:

Question: In an a.c. circuit with phase voltage V and current I, the power dissipated is

a)

b)

c)

d) None of these

Answer:

Question:

a) 0.80
b) 0.33
c) 0.56
d) 0.64
Answer: 0.80

Question:

a)

b)

c)

d)

Answer:

Question: In an LCR series resonant circuit, the capacitance is changed from C to 4C. For the same resonant frequency, the inductance should be changed from L to

a)

b)

c) 4 L

d) 2 L

Answer:

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
Answer: 20 ohm

Question: Resonance frequency of LCR series a.c. circuit is f0. Now the capacitance is made 4 times, then the new resonance frequency will become

a)

b)

c)

d) None of these

Answer:

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) 0 V
b) 100 V
c) None of these
d) 50 V
Answer: 0 V

Question: 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 incorrect, reason is correct.
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 correct, reason is correct; reason is a correct explanation for assertion
Answer: Assertion is incorrect, reason is correct.