Question 15: An ac source is connected to a capacitor C. Due to decrease in its operating frequency :
(1) displacement current decreases.
(2) capacitive reactance remains constant
(3) capacitive reactance decreases.
(4) displacement current increases.
Answer: Option (1)
Explanation:
For a capacitor connected to an alternating current source, the capacitive reactance is given by
X_{C}=\frac{1}{\omega C}=\frac{1}{2\pi f C}When the operating frequency f decreases,
the capacitive reactance X_{C} increases.
The current through the capacitor is given by
I=\frac{V}{X_{C}}As X_{C} increases due to decrease in frequency,
the current flowing through the capacitor decreases.
The displacement current in a capacitor is equal to the current in the external circuit.
Therefore, when the operating frequency decreases, the displacement current also decreases.
Hence, the correct answer is Option (1).