Question 173: EM waves

Question

The intensity of the light from a bulb incident on a surface is 0.22 W/m
2
. 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
C
2
N
$$-$$1
-m
$$-$$2
, speed of light in vacuum c = 3 $$	imes$$ 10
8
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/m 2 . The amplitude of the magnetic field in this light-wave is ______________ $\times 10 -9 T. (Given : Permittivity of vacuum \in 0 = 8.85 \times 10 -12 C 2 N -1 -m -2 , speed of light in vacuum c = 3 \times 10 8 ms -$1 )

Integer / Numeric Answer Type