Question

An antenna uses electromagnetic waves of frequency 5 MHz. For proper working, the size of the antenna should be

• A. 15 km
• B. 15 m
• C. 3 km
• D. 300 m

Answer 1

Answer: (B)

15 m

Answer 2

$C=f \lambda$
$\lambda=\frac{C}{f}=\frac{3\times10^{8}}{5\times10^{6}}=10^{2}=60m$
The antenna length should be $\frac{\lambda}{4}=\frac{60}{4}=15 m$