AC Voltage Applied to an Inductor - Class 12 Physics MCQ

This set of Class 12 Physics Chapter 7 Multiple Choice Questions & Answers (MCQs) focuses on “AC Voltage Applied to an Inductor”.

1. What is the reactance of an inductor in a dc circuit?
a) Maximum
b) Minimum
c) Zero
d) Indefinite
View Answer

Answer: c
Explanation: The reactance of an inductor in a dc circuit is zero.
For dc ➔ f = 0
X_L = 2π f L
X_L = 0
Therefore, the reactance of an inductor in a dc circuit is zero.

2. In which type of circuit the value of power factor will be minimum?
a) Resistive
b) Inductive
c) Superconductive
d) Semi conductive
View Answer

Answer: b
Explanation: For a purely inductive circuit, Φ = ± \(\frac {\pi }{2}\)
Power factor = cos (±\(\frac {\pi }{2}\))
Power factor = 0
Therefore, the power factor will be minimum for an inductive circuit.

3. The frequency of ac is doubled. How does X_L get affected?
a) X_L gets doubled
b) X_L becomes zero
c) X_L is halved
d) X_L is indefinite
View Answer

Answer: a
Explanation: When the frequency of an ac is doubled ➔ The inductive reactance (X_L) gets doubled.
This is because inductive reactance is directly proportional to the frequency of an alternating current circuit.

4. At what frequency will a coil, which has an inductance of 2.5 H, have a reactance of 3500 Ω?
a) 700Hz
b) 350 Hz
c) 200 Hz
d) 223 Hz
View Answer

Answer: d
Explanation: f = \(\frac {X_L}{2\pi L}\)
f = \(\frac {3500}{(2 \times 3.14 \times 2.5)}\)
f = 222.9 Hz ≈ 223 Hz
Therefore, the frequency of a coil having reactance of 3500 Ω is 223 Hz.

5. Why does an inductor offer an easy path to dc and a resistive path to ac?
a) X_L is maximum for dc and infinite for ac
b) X_L is zero for dc and infinite for ac
c) X_L is zero for dc and finite for ac
d) X_L is maximum for dc and finite for ac
View Answer

Answer: c
Explanation: For dc, f = 0,
X_L = 2π f L
X_L = 0
X_L is zero for dc and has a finite value for ac Hence an inductor offers an easy path to dc and a resistive path to ac.

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6. The inductive reactance for an ac circuit containing only an inductor is \(\frac {E_0}{X_L}\).
a) True
b) False
View Answer

Answer: b
Explanation: No, this statement is false. The inductive reactance for an ac circuit containing only an inductor is X_L = ωL.
X_L = ωL
X_L = 2π f L

7. Determine the peak current if an inductor of inductance 500 mH is connected to an ac source of peak emf 650 V and frequency 100 Hz
a) 1.55 A
b) 2.07 A
c) 7.89 A
d) 9.87 A
View Answer

Answer: b
Explanation: Peak current (I₀) = \(\frac {E_0}{X_L}\)
I₀ = \(\frac {650}{(2 \times 3.14 \times 100 \times 0.5)}\)
I₀ = 2.07 A
Therefore, the peak current is calculated as 2.07 A.

8. Find out the rms value of current in the circuit wherein a 35 mH inductor is connected to 200 V, 70 Hz ac supply.
a) 13 A
b) 15 A
c) 20 A
d) 45 A
View Answer

Answer: a
Explanation: X_L = 2π f L
X_L = 2π × 70 × 35 × 10^-3 Ω.
I_rms = \(\frac {E_{rms}}{X_L} = \frac {200}{(2\pi \times 70 \times 35 \times 10^{-3})}\)
I_rms = 12.99 A ≈ 13 A
Therefore, the rms value of current in the circuit is 13 A.

Sanfoundry Global Education & Learning Series – Physics – Class 12.

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