A lamp emits monochromatic green light uniformly in all directions. lamp is 3% efficient in converti

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8.Electromagnetic waves

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A lamp emits monochromatic green light uniformly in all directions. The lamp is $3%$ efficient in converting electrical power to electromagnetic waves and consumes $100\,W $ of power. The amplitude of the electric field associated with the electromagnetic radiation at a distance of $10m$ from the lamp will be........$V/m$

A

$1.34$

B

$2.68$

C

$5.36$

D

$9.37$

Solution

(a)${S_{av}} = \frac{1}{2}{\varepsilon _0}cE_0^2 = \frac{P}{{4\pi {R^2}}}$
==> ${E_0} = \sqrt {\frac{P}{{2\pi {R^2}{\varepsilon _0}C}}} $
$ = \sqrt {\frac{3}{{2 \times 3.14 \times 100 \times 8.85 \times {{10}^{ – 12}} \times 3 \times {{10}^8}}}} $
$= 1.34\, V/m$

Standard 12

Physics

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