physics : class12 Phasor Representation : Wattless Current : Electromagnetic Induction and Alternating Currents MCQ Questions and Answers
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Phasor Representation
MCQ questions and answers.
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MCQ Questions
1. In a phasor diagram for a purely inductive AC circuit, the current phasor lags the voltage phasor by:
A.
0°
B.
45°
C.
90°
D.
180°
Correct Answer:
90°
Explanation:
For a purely inductive circuit, the current phasor lags the voltage phasor by 90°. This phase difference represents wattless current.
2. In a phasor diagram for a purely capacitive AC circuit, the current phasor leads the voltage phasor by:
A.
0°
B.
90°
C.
120°
D.
180°
Correct Answer:
90°
Explanation:
In a purely capacitive circuit, the current phasor leads the voltage phasor by 90°, so the average power is zero.
3. Which phasor relationship represents a purely resistive AC circuit?
A.
Voltage and current phasors are in phase
B.
Current phasor leads voltage by 90°
C.
Current phasor lags voltage by 90°
D.
Voltage and current phasors are opposite in phase
Correct Answer:
Voltage and current phasors are in phase
Explanation:
For a purely resistive circuit, voltage and current reach their maximum and zero values together, so their phasors are in phase.
4. A voltage phasor is taken as the reference along the positive horizontal axis. In a purely inductive circuit, the current phasor should be drawn along the:
A.
Positive horizontal axis
B.
Negative horizontal axis
C.
Positive vertical axis
D.
Negative vertical axis
Correct Answer:
Negative vertical axis
Explanation:
The current lags the voltage by 90° in an inductive circuit. Therefore, when voltage is along the positive horizontal axis, current points along the negative vertical axis.
5. A voltage phasor is taken as the reference along the positive horizontal axis. In a purely capacitive circuit, the current phasor should be drawn along the:
A.
Positive vertical axis
B.
Negative vertical axis
C.
Positive horizontal axis
D.
Negative horizontal axis
Correct Answer:
Positive vertical axis
Explanation:
The current leads the voltage by 90° in a capacitive circuit. Hence, the current phasor is drawn along the positive vertical axis when voltage is the reference.
6. If the voltage and current phasors are perpendicular to each other, the average power consumed is:
A.
Maximum
B.
Zero
C.
Half of the maximum power
D.
Equal to the peak voltage
Correct Answer:
Zero
Explanation:
Perpendicular voltage and current phasors indicate a phase difference of 90°. Since the power factor is cos 90°, the average power is zero.
7. The angle between voltage and current phasors in a wattless AC circuit is:
A.
0°
B.
30°
C.
60°
D.
90°
Correct Answer:
90°
Explanation:
Wattless current occurs when voltage and current differ in phase by 90°, making their average power product zero.
8. In a phasor diagram, the resultant voltage in a series circuit containing resistance and inductance is obtained by:
A.
Adding the voltage phasors algebraically
B.
Adding the voltage phasors vectorially
C.
Subtracting current from voltage
D.
Multiplying the voltage phasors
Correct Answer:
Adding the voltage phasors vectorially
Explanation:
Phasors represent magnitude and phase, so the resistor and inductor voltage drops must be combined using vector addition.
9. In the phasor representation of a series R-L circuit, the voltage across the resistor is:
A.
In phase with the current
B.
90° behind the current
C.
90° ahead of the current
D.
Opposite in phase to the current
Correct Answer:
In phase with the current
Explanation:
For a resistor, voltage and current are in phase. Thus, the resistor voltage phasor is drawn in the same direction as the current phasor.
10. In the phasor representation of a series R-C circuit, the voltage across the capacitor is:
A.
In phase with the current
B.
90° ahead of the current
C.
90° behind the current
D.
Opposite in phase to the current
Correct Answer:
90° behind the current
Explanation:
In a capacitor, current leads voltage by 90°. Therefore, the capacitor voltage phasor lags the current phasor by 90°.
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Phasor Representation
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