Question

The mean intensity of radiation on the surface of the Sun is about 10⁸ W/m². The rms value of the corresponding magnetic field is closet to :
(A) 1 T (B) 10² T
(C) 10⁻²T (D) 10⁻⁴ T

Answer 1

Intensity of EM wave -

I = \frac{1}{2} \epsilon _{o} E_{o}^{2}c

- wherein

\epsilon _{o} = Permittivity of free space

E _{o} = Electric field amplitude

c = Speed of light in vacuum

I = 108 w/m2

I =\frac{1}{2} \epsilon _{o} E_{o}^{2}c= \varepsilon_{0}.CE^{2}rms............1

E_{rms} = CB_{rms}...........2

from 1 and 2

I=\varepsilon _{0}C^{3}B^{2}_{rms}

B_{rms} = \sqrt{\frac{I}{\varepsilon _{0}C^{3}}}= \sqrt{\frac{10^8}{8.85\times 10^{-12}\times \left ( 3\times 10^{8} \right )^{3}}}\approx 10^{-4}T