Question

The capacitive reactance at 1600Hz is 81 $\Omega$ .When the frequency is doubled then the capacitive reactance will be:

• A. 40.5$\Omega$
• B. 81$\Omega$
• C. 162$\Omega$
• D. zero

Answer 1

Answer: (A)

40.5$\Omega$

Capacitive reactance = $\frac{1}{\omega C}=\frac{1}{2\pi fC}$
$81=\frac{1}{2\pi \times 1600C}$
$C=\frac{1}{2\pi \times 1600\times 81}$
Capacitive reactance = $\frac{1}{\omega C}=\frac{1}{2\pi fC}$
$81=\frac{1}{2\pi \times 2\times 1600\times \frac{1}{2\pi \times 1600\times 81}}$
$C=\frac{81}{2}=40.5\Omega$