AC Voltage Applied to a Resistor - Class 12 Physics MCQ

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

1. What is the rms value of the current, if its instantaneous current value is 8 sin314 t?
a) 2√4 A
b) 10 A
c) 4√2 A
d) 50 A
View Answer

Answer: c
Explanation: I = I₀ sinωt.
I_rms = \(\frac {I_0}{\sqrt {2}}\)
I_rms = \(\frac {8}{(\sqrt {2})}\)
I_rms = 4√2 A

2. What will be the rms value of the voltage, if the sinusoidal value voltage is given as E = 100 sin 314 t applied across a resistor of resistance 15 ohms?
a) 200 V
b) 70.71 V
c) 100 V
d) 33.87 V
View Answer

Answer: b
Explanation: E = E₀ sinωt.
E_rms = \(\frac {E_0}{\sqrt {2}}\)
E_rms = \(\frac {100}{\sqrt {2}}\)
E_rms = 70.71 V

3. Determine the rms value of current in the circuit if a 50 Ω resistor is connected across an ac source of 200 V, 50 Hz?
a) 4 A
b) 200 A
c) 50 A
d) 1 A
View Answer

Answer: a
Explanation: I_rms = \(\frac {E_{rms}}{R}\)
I_rms = \(\frac {200}{50}\)
I_rms = 4 A

4. Calculate the rms voltage, if the peak value of an a.c. supply is 300 V.
a) 561.4 V
b) 969.2 V
c) 625.1 V
d) 212.1 V
View Answer

Answer: d
Explanation: E₀ = 300 V
E_rms = 0.707 E₀
E_rms = 0.707 × 300
E_rms = 212.1 V

5. Find out the net power consumed over a full cycle, if a 150 Ω resistor is connected to a 350 V, 100 Hz ac supply.
a) 2.3 W
b) 350 W
c) 805 W
d) 500 W
View Answer

Answer: c
Explanation: I_rms = \(\frac {E_{rms}}{R}\).
I_rms = \(\frac {350}{150}\)
I_rms = 2.3 A.
P_av = E_rms I_rms
P_av = 350 × 2.3
P_av = 805 W

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6. When a sinusoidal voltage E = 200 sin 314 t is applied to a resistor of 10 Ω resistance, the power dissipated is 250 Watts.
a) True
b) False
View Answer

Answer: a
Explanation: Yes, this is a true statement. The explanation is given as follows:
E = E₀ sinωt.
E_rms = \(\frac {E_0}{\sqrt {2}} = \frac {50}{\sqrt {2}}\)
E_rms = 35.35 V.
I_rms = \(\frac {E_{rms}}{R} \, = \, \frac {35.5}{5} \)
I_rms = 7.07 A.
Power dissipated = E_v × I_v = 35.35 × 7.07
Power dissipated = 249.92 W ≈ 250 W.

7. Which value of the current do you measure with an a.c. ammeter?
a) Instantaneous current
b) Root mean square value
c) Electromotive force
d) Peak current
View Answer

Answer: b
Explanation: Root mean square value of the current can be measured with the help of an a.c. ammeter. It is used to measure the alternating current that flows through any branch of an electric circuit is called AC ammeter.

8. Calculate the value of the peak current, if the rms value of current in an ac circuit is 50 A?
a) 70.7 A
b) 65 A
c) 50 A
d) 1 A
View Answer

Answer: a
Explanation: I_rms = 50 A.
I₀ = √2 I_rms
I₀ = 1.414 × 50
I₀ = 70.7 A
Therefore, the peak current is 70.7 A.

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