1. What is the apparent power in an AC circuit?
A.
The product of rms voltage and rms current
B.
The difference between voltage and current
C.
The product of resistance and current
D.
The ratio of voltage to current
Correct Answer:
The product of rms voltage and rms current
Explanation:
Apparent power is given by S = V_rms I_rms, where V_rms is the rms voltage and I_rms is the rms current.
2. What is the SI unit of apparent power?
A.
Watt
B.
Volt-ampere
C.
Joule
D.
Ohm
Correct Answer:
Volt-ampere
Explanation:
Apparent power is measured in volt-amperes (VA), obtained by multiplying rms voltage in volts by rms current in amperes.
3. An AC circuit has an rms voltage of 100 V and an rms current of 2 A. What is its apparent power?
A.
50 VA
B.
98 VA
C.
200 VA
D.
102 VA
Correct Answer:
200 VA
Explanation:
Using S = V_rms I_rms, the apparent power is 100 × 2 = 200 VA.
4. An AC appliance draws an rms current of 5 A from a 220 V supply. What is its apparent power?
A.
44 VA
B.
225 VA
C.
1100 VA
D.
1110 VA
Correct Answer:
1100 VA
Explanation:
The apparent power is S = V_rms I_rms = 220 × 5 = 1100 VA.
5. If the rms voltage in an AC circuit is doubled while the rms current remains constant, what happens to the apparent power?
A.
It becomes half
B.
It remains unchanged
C.
It becomes double
D.
It becomes four times
Correct Answer:
It becomes double
Explanation:
Since S = V_rms I_rms, doubling the voltage while keeping current constant doubles the apparent power.
6. A circuit has an apparent power of 600 VA and an rms voltage of 120 V. What is the rms current?
A.
0.2 A
B.
5 A
C.
480 A
D.
720 A
Correct Answer:
5 A
Explanation:
From S = V_rms I_rms, I_rms = S / V_rms = 600 / 120 = 5 A.
7. A purely inductive AC circuit has an rms voltage of 50 V and an rms current of 4 A. What is its apparent power?
A.
0 VA
B.
12.5 VA
C.
46 VA
D.
200 VA
Correct Answer:
200 VA
Explanation:
Even though a purely inductive circuit has wattless current, its apparent power is S = V_rms I_rms = 50 × 4 = 200 VA.
8. The apparent power of an AC circuit is 1000 VA, and its rms current is 10 A. What is the rms voltage?
A.
10 V
B.
100 V
C.
990 V
D.
10000 V
Correct Answer:
100 V
Explanation:
Using V_rms = S / I_rms, the rms voltage is 1000 / 10 = 100 V.
9. Which expression represents the apparent power of an AC circuit in terms of its rms voltage and rms current?
A.
S = V_rms + I_rms
B.
S = V_rms / I_rms
C.
S = V_rms I_rms
D.
S = V_rms - I_rms
Correct Answer:
S = V_rms I_rms
Explanation:
Apparent power is the product of the rms voltage and rms current: S = V_rms I_rms.
10. An AC circuit has an rms voltage of 240 V and an rms current of 0.5 A. What is its apparent power?
A.
120 VA
B.
240.5 VA
C.
480 VA
D.
1200 VA
Correct Answer:
120 VA
Explanation:
The apparent power is S = V_rms I_rms = 240 × 0.5 = 120 VA.
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