# MCQ Questions for Class 12 Physics Chapter 7 Alternating Current with Answers

Do you need help learning for your Class 12 Physics exam? Students may want to download NCERT MCQ Questions for Class 12 Physics Chapter 7 Alternating Current with Answers Pdf free download. This Alternating Current Class 12 MCQs Questions with Answers can help understand the concepts score better in your Class 12 Physics Exam, so make sure you practice these! Check out chapter-wise MCQ Questions for Class 12 Physics with Answers.

## Alternating Current Class 12 MCQs Questions with Answers

Solve this Alternating Current Multiple Choice Questions of Class 12 Physics Chapter 7 MCQ, so as not to miss out on any concept from being clear about what they mean!

Question 1.
If the rms current in a 50 Hz ac circuit is 5 A, the value of the current 1/300 second after its value becomes zero is
(a) 5√2A
(b) 5√3 /2 A
(c) 5/6 A
(d) 5/√2 A

Question 2.
To reduce the resonant frequency in an LCR series circuit with a generator
(a) the generator frequency should be reduced.
(b) another capacitor should be added in parallel to the first.
(c) the iron core of the inductor should be removed.
(d) dielectric in the capacitor should be removed.

Answer: (b) another capacitor should be added in parallel to the first.

Question 3.
The output of a step-down transformer is measured to be 24 V when connected to a 12 watt light bulb. The value of the peak current is
(a) 1/√2A
(b) √2A
(c) 2A
(d) 2√V2A

Question 4.
In an alternating current circuit consisting of elements in series, the current increases on increasing the frequency of supply. Which of the following elements are likely to constitute the circuit?
(a) Only resistor.
(b) Resistor and an inductor.
(c) Capacitor and an inductor.
(d) Only a capacitor.

Question 5.
As the frequency of an ac circuit increases, the current first increases and then decreases. What combination of circuit elements is most likely to comprise the circuit?
(a) Inductor and capacitor.
(b) Resistor and inductor.
(c) Resistor and capacitor.
(d) None.

Question 6.
When an AC voltage of 220 V is applied to the capacitor C
(a) the maximum voltage between plates is 220 V.
(b) the current is in phase with the applied voltage.
(c) the charge on the plates is out of phase with the applied voltage.
(d) power delivered to the capacitor is zero.

Answer: (d) power delivered to the capacitor is zero.

Question 7.
Electrical energy is transmitted over large distances at high alternating voltages. Which of the following statements is incorrect?
(a) For a given power level, there is a lower current.
(b) Lower current implies less power loss.
(c) Transmission lines can be made thinner.
(d) It is easy to reduce the voltage at the receiving end using step-down transformers.

Question 8.
In an ac circuit, V and i are given by V = 100 sin (100 t) volt and i = 100 sin (100 + $$\frac { π }{3}$$) mA. The power dissipated in circuit is
(a) 104 W
(b) 10 W
(c) 2.5 W
(d) 5 W

Question 9.
A small signal voltage V(t) = V0 sinω t is applied across an ideal capacitor C
(a) Current l (t) lags voltage V(t) by 90°.
(b) Over a full cycle the capacitor C does not consume any energy from the voltage source.
(c) Current l(t) is in phase with voltage V(t).
(d) Current l(t) leads voltage V(t) by 180°.

Answer: (b) Over a full cycle the capacitor C does not consume any energy from the voltage source.

Question 10.
The potential differences across the resistor, capacitor and inductor are 80 V, 40 V and 100 V, respectively in an LCR circuit. The power factor of this circuit is:
(a) 0.8
(b) 1.0
(c) 0.4
(d) 0.5

II. Fill in the Blanks

Question 1.
A steady (dc) current which when passed through a circuit for half the time period of ac will send the same amount of charge as is sent by ac through the same circuit for the same time is called ……………….

Answer: Average or mean value of ac

Question 2.
A steady current (dc) which when passed through a resistor in a given time produces the same heat as is produced by the ac. when passed through the same resistor for the same time is called ……………….

Answer: Root mean square value of ac

Question 3.
When ac flows through a pure resistor, emf and current are in ……………..

Question 4.
When ac flows through a pure inductor, emf …………….. current by an angle π/2.

Question 5.
When ac flows through a pure capacitor, emf ……………… current by an angle π/2.

Question 6.
…………….. is the ratio of the rms value to the mean or average value of ac.

Question 7.
AC flows only on the surface of a wire. This effect is called ……………….. “effect”.

Question 8.
In ac-circuit, the average power consumed by a pure capacitor during one cycle in pure capacitance is ………………..

Question 9.
In ac-circuit, the average power consumed by a pure inductor during one cycle in pure capacitance is ………………..

Question 10.
If the power loss in a circuit is zero, the current is called ………………

Question 11.
A choke is preferred over resistance in an ac-circuit to decrease ac-current because it consumes practically ……………… power.

Question 12.
At resonance the current in a circuit is ……………..

Question 13.
At resonance an LCR circuit behaves as a pure ……………….. circuit.

Question 14.
The ratio $$\frac { ω_0 }{Δω}$$ is called ……………….

Question 15.
Average power is equal to the product of virtual power and ………………

Question 16.
……………….. is a device to convert a low voltage at high current, to a high voltage at low current and vice versa.

Question 17.
AC dynamo is based on the principle of …………….. induction.

Question 18.
An ac dynamo has ………………. rings.

Question 19.
Maximum emf Induced in an ac dynamo is ……………………