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 ______× 10–9 T. - Physics (JEE Main)

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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 ______× 10–9 T. 

(Given: Permittivity of vacuum ε0 = 8.85 × 10–12 C2 N–1 – m–2, speed of light in vacuum c = 3 × 108 ms-1)

Options

  •  46 × 10–9 T

  •  42 × 10–9 T

  •  45 × 10–9 T

  •  43 × 10–9 T

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Solution

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 43 × 10–9 T. 

Explanation:

As I = `(1/2 epsilon_0"E"_0^2)`

On substituting value of I, ε0 and c, we get

0.22 = `1/2 (8.85 xx 10^-12) "E"_0^2xx3xx10^8`

E= `sqrt((2xx0.22)/(8.85xx10^-12xx3xx10^8))`

= 12.9 N/C

As c = `"E"_0/"B"_0`

⇒ B0 = `12.9/(3xx10^8)`

= 4.3 × 10–8

= 43 × 10–9 T

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