First slide

Average energy density of electromagnetic wave

Question

An electromagnetic wave is propagating in a medium. If intensity of wave is 1200 $\frac{W}{m^{2}}$ and average energy density is $6 μ J / m^{3}$ , find the refractive index of the medium.

Moderate

A

1.82
B

1.45
C

1.5
D

1.65

Solution

$u = 6 \times 10^{- 6} J / m^{3} a n d I = 1200 W / m^{2}$
$∴$ Speed of the wave in the medium $v = \frac{I}{u} = 1200 / 6 \times 10^{- 6} \frac{m}{s}$
$\Rightarrow v = 2 \times 10^{8} m / s$
$∴$ Refractive index, $μ = \frac{C}{v} = \frac{3 \times 10^{8}}{2 \times 10^{8}} = 1.5$

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