Q. Calculate the phase velocity of electromagnetic wave having electron density and frequency of D-layer, $N = 400$ electron $cc^{- 1},\ v = 200$ kHz
A) $3 \times 10^{8}ms^{- 1}$
B) $3.5 \times 10^{8}ms^{- 1}$
C) $6.9 \times 10^{8}ms^{- 1}$
D) $1.1 \times 10^{9}ms^{- 1}$
Explanation
(c) $\mu = \sqrt{1 - \frac{81.45N}{v^{2}}}$
$= \sqrt{1 - \frac{81.45 \times 400 \times 10^{6}}{\left( 200 \times 10^{3} \right)^{2}}} = 0.43$
$\mu = \frac{c}{v}$
$\therefore$ Phase velocity, $v = \frac{c}{\mu} = \frac{3 \times 10^{8}}{0.43}$
$= 6.98 \times 10^{8}ms^{- 1}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.