A transmitting station transmits radio waves of wavelength 300 m. The inductance of the coil required with a capacitor of capacity 1.0 μF in a resonant circuit will be
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → $2.53 × 10^{-8} H$
Given:
Wavelength, $\lambda = 300\ \text{m}$
Capacitance, $C = 1.0\ \mu\text{F} = 1.0 \times 10^{-6}\ \text{F}$
Speed of light, $c = 3 \times 10^8\ \text{m/s}$
Frequency of wave: $f = \frac{c}{\lambda} = \frac{3 \times 10^8}{300} = 1 \times 10^6\ \text{Hz}$
For resonance in an LC circuit:
$f = \frac{1}{2\pi \sqrt{LC}}$
Rearrange for $L$:
$L = \frac{1}{(2\pi f)^2 C}$
Substitute values:
$L = \frac{1}{(2\pi \cdot 10^6)^2 \cdot 1 \times 10^{-6}}$
$L = \frac{1}{4\pi^2 \cdot 10^{12} \cdot 10^{-6}}$
$L = \frac{1}{4\pi^2 \cdot 10^6}$
$L \approx \frac{1}{39.5 \cdot 10^6} \approx 2.53 \times 10^{-8}\ \text{H}$