1. What is meant by wattless current in an AC circuit?
A.
A current that produces zero average power
B.
A current that produces maximum heat
C.
A current that always remains constant
D.
A current that flows only in a DC circuit
Correct Answer:
A current that produces zero average power
Explanation:
Wattless current is an alternating current whose average power consumption over a complete cycle is zero.
2. In a circuit carrying wattless current, the average power consumed is:
A.
One watt
B.
Zero
C.
Maximum
D.
Negative
Correct Answer:
Zero
Explanation:
The defining feature of wattless current is that it consumes no average power.
3. Wattless current flows when the phase difference between voltage and current is:
A.
0 degrees
B.
45 degrees
C.
90 degrees
D.
180 degrees
Correct Answer:
90 degrees
Explanation:
For wattless current, voltage and current differ in phase by 90 degrees, making the average power zero.
4. The power factor of a circuit carrying purely wattless current is:
A.
Unity
B.
0.5
C.
Zero
D.
One
Correct Answer:
Zero
Explanation:
Power factor is cos phi. For wattless current, phi is 90 degrees, so cos phi equals zero.
5. Which type of circuit ideally carries wattless current?
A.
Purely resistive circuit
B.
Purely inductive circuit
C.
Circuit containing only a battery
D.
Circuit with a filament lamp
Correct Answer:
Purely inductive circuit
Explanation:
In a purely inductive circuit, current and voltage differ by 90 degrees, so the current is wattless.
6. A purely capacitive circuit carries wattless current because:
A.
Its current is in phase with voltage
B.
Its resistance is extremely high
C.
Its current differs in phase from voltage by 90 degrees
D.
It does not allow alternating current to flow
Correct Answer:
Its current differs in phase from voltage by 90 degrees
Explanation:
In a purely capacitive circuit, the 90-degree phase difference causes zero average power consumption.
7. Which expression represents the average power for wattless current?
A.
P = VI
B.
P = VI sin phi
C.
P = VI cos phi, with phi equal to 90 degrees
D.
P = V divided by I
Correct Answer:
P = VI cos phi, with phi equal to 90 degrees
Explanation:
Average AC power is VI cos phi. For wattless current, phi is 90 degrees and cos phi is zero.
8. In wattless current, electrical energy is ideally:
A.
Completely converted into heat
B.
Stored and returned without average consumption
C.
Permanently lost in the circuit
D.
Converted into chemical energy
Correct Answer:
Stored and returned without average consumption
Explanation:
In an ideal inductive or capacitive circuit, energy is temporarily stored and returned to the source, resulting in zero average power.
9. Which statement correctly describes wattless current?
A.
It has no instantaneous value at any time
B.
It has zero average power but may have a nonzero instantaneous value
C.
It can flow only through a resistor
D.
It always has a power factor of one
Correct Answer:
It has zero average power but may have a nonzero instantaneous value
Explanation:
Wattless current can flow through the circuit, but its average power over a complete cycle is zero.
10. Wattless current is also associated with a circuit having:
A.
Only reactive opposition to current
B.
Only resistance and no reactance
C.
No voltage across its elements
D.
A phase difference of zero between voltage and current
Correct Answer:
Only reactive opposition to current
Explanation:
An ideal inductor or capacitor provides reactance without consuming average power, producing wattless current.
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