9. A capacitor of capacity C and reactance X if capacitance and frequency become double then reactance will be: (2001)
Solution:
Capacitive reactance is $X = \frac{1}{2\pi f C}$. When capacitance becomes $2C$ and frequency becomes $2f$, the new reactance is $X' = \frac{1}{2\pi(2f)(2C)} = \frac{1}{4(2\pi f C)} = \frac{X}{4}$.
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