# The intensity of the sunlight reaching the earth is $1380\; W/m^2$. Calculate the amplitude of the magnetic field in the light wave. Assume the light to be a plane monochromatic wave.

$\begin {array} {1 1} (a)\;3.4 \times 10^{-6}T & \quad (b)\;34 \times 10^{-8}T \\ (c)\;3.4 \times 10^{-8}T & \quad (d)\;34\: \mu \: T \end {array}$

$E_o = \sqrt{\large\frac{2\: I}{\in_oc}}$$= \sqrt {\bigg[\large\frac{2 \times 1380}{\bigg(8.85 \times 10^{-12} \times 3 \times 10^8 \bigg)} \bigg]}$$= 1.02 \times 103N/C$
So, $B_o =\large\frac{ E_o}{c} = \large\frac{1.02 \times 10^3}{3 \times 10^8T }= 3.4 \times 10^{-6}T$
Ans : (a)