Question 171: EM waves

Question

The intensity of the light from a bulb incident on a surface is 0.22 W/m2. The amplitude of the magnetic field in this light-wave is ______________ $$	imes$$ 10$$-$$9 T.
(Given : Permittivity of vacuum $$\in$$0 = 8.85 $$	imes$$ 10$$-$$12 C2 N$$-$$1-m$$-$$2, speed of light in vacuum c = 3 $$	imes$$ 108 ms$$-$$1)

Accepted Answer

$$I = {1 \over 2}{\varepsilon _0}E_0^2\,.\,c = {1 \over 2}{\varepsilon _0}{(c{B_0})^2}c$$
$$ \Rightarrow I = {1 \over 2}{\varepsilon _0}{c^3}B_0^2$$
$$ \Rightarrow 0.22 = {1 \over 2}\left( {8.85 	imes {{10}^{ - 12}}} ight){\left( {3 	imes {{10}^8}} ight)^3}B_0^2$$
$$ \Rightarrow {B_0} \simeq 43 	imes {10^{ - 9}}$$ T

EM waves

The intensity of the light from a bulb incident on a surface is 0.22 W/m2. The amplitude of the magnetic field in this light-wave is ______________ $\times 10-9 T. (Given : Permittivity of vacuum \in0 = 8.85 \times 10-12 C2 N-1-m-2, speed of light in vacuum c = 3 \times 108 ms-$1)

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