Electromagnetic Waves Question 7
Question 7 - 2024 (31 Jan Shift 1)
In a plane EM wave, the electric field oscillates sinusoidally at a frequency of $5 \times 10^{10} Hz$ and an amplitude of $50 Vm^{-1}$. The total average energy density of the electromagnetic field of the wave is : [Use
$\left.\varepsilon _0=8.85 \times 10^{-12} C^{2} / Nm^{2}\right]$
(1) $1.106 \times 10^{-8} Jm^{-3}$
(2) $4.425 \times 10^{-8} Jm^{-3}$
(3) $2.212 \times 10^{-8} Jm^{-3}$
(4) $2.212 \times 10^{-10} Jm^{-3}$
Show Answer
Answer: (1)
Solution:
$U _E=\frac{1}{2} \epsilon _0 E^{2}$
$U _E=\frac{1}{2} \times 8.85 \times 10^{-12} \times(50)^{2}$
$=1.106 \times 10^{-8} J / m^{3}$
