Q. In a plane electromagnetic wave electric field varies with time having an amplitude $1\ Vm^{- 1}$. The frequency of wave is $0.5 \times 10^{15}$ Hz. The wave is propagation along $X$-axis. What is the average energy density of magnetic field?
A) $1.1 \times 10^{- 12}J\ m^{- 3}$
B) $2.2 \times 10^{- 12}J\ m^{- 3}$
C) $3.3 \times 10^{- 12}J\ m^{- 3}$
D) $4.4 \times 10^{- 12}J\ m^{- 3}$
Explanation
(b) In an electromagnetic wave, the average energy density of magnetic field $\mu_{B} =$ average energy density of electric filed $v_{E} = \frac{1}{4}\varepsilon_{0}E_{0}^{2}$
$= \frac{1}{4} \times (8.85 \times 10^{- 12}) \times 1^{2}$
$= 2.21 \times 10^{- 12}\ Jm^{- 3}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.