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 ______× 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

Answer 1

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`

E₀ = `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