Question

The magnetic field in a plane electromagnetic wave is given by $=2\times 10^{-7}\sin \left(0.5\times 10^{3}x+1.5\times 10^{11}t\right)$. This electromagnetic wave is

• A. Visible light
• B. Infrared
• C. Microwave
• D. Radiowave

Answer 1

Answer: (D)

$B=2\times 10^{-7}\sin \left(0.5\times 10^{-3}x+1.5\times 10^{11}t\right)$
$f=\frac{c}{\lambda },$
$k=0.5\times 10^{-3}$
$\omega =1.5\times 10^{11}$
$V=\frac{\omega }{k}=\frac{1.5\times 10^{11}}{0.5\times 10^{-3}}$
$=3\times 10^{14}$
$\frac{\omega }{k}=f\lambda$
$k=\frac{2\pi }{\lambda }$
$\therefore \lambda =\frac{2\pi }{k}=\frac{2\times 22}{7\times 0.5\times 10^{-3}}$
$=\underset{\text{Radio waves}}{1.25\times 10^{4}m}$