An alternating voltage source is connected to a resistor R, and a capacitor C, then which of the following statements about phase angle between voltage V and current I is correct?
Correct answer: C. In the resistor, I and V are in phase - In the capacitor, I leads V by 90 degrees
- A. In the resistor, I leads V by 90 degrees - In the capacitor, I leads V by 90 degrees
- B. In the resistor, I lags V by 90 degrees - In the capacitor, I leads V by 90 degrees
- C. In the resistor, I and V are in phase - In the capacitor, I leads V by 90 degrees
- D. In the resistor, I and V are in phase - In the capacitor, I lags V by 90 degrees
- E. In the resistor, I lags V by 90 degrees - In the capacitor, I lags V by 90 degrees
Explanation
In a resistor, the current and voltage are in phase because the current flows in the same direction as the voltage. However, in a capacitor, the current leads the voltage by 90 degrees because the capacitor initially resists the flow of current and stores energy in its electric field. As the voltage across the capacitor increases, the current begins to flow, and it reaches its maximum value when the voltage is at its minimum value. Therefore, the current leads the voltage by 90 degrees in a capacitor.
This question appeared on the NUMS 2019 (cancelled sitting) paper, which you can sit online with every answer explained.
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About AC Through Resistor, Capacitor and Inductor
Alternating current through a resistor, capacitor and inductor involves phase relationships between voltage and current, reactance, impedance and energy transfer. A resistor keeps voltage and current in phase, while a capacitor and inductor produce opposite phase shifts, a distinction used in circuit diagrams and numerical calculations.
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