Question

The mean intensity of radiation on the surface of the Sun is about ${10}^8{\text{Wm}}^{-2}$. The $rms$ value of the corresponding magnetic field is closest to:

• A. ${10}^2\text{T}$
• B. $1\text{T}$
• C. ${10}^{-2}\text{T}$
• D. ${10}^{-4}\text{T}$

Answer 1

The correct option is D ${10}^{-4}\text{T}$

The intensity of the electromagnetic wave is given by,

$I=\frac{B_0^2}{2{\mu }_0}\cdot c$
$\Rightarrow {\left(\frac{B_0}{\sqrt{2}}\right)}^2=\frac{I{\mu }_0}{c}$
$\Rightarrow B_{rms}=\sqrt{\frac{I{\mu }_0}{c}}$
$\Rightarrow B_{rms}=\sqrt{\frac{{10}^8\times 4\pi \times {10}^{-7}}{3\times {10}^8}}$
Which is closest to ${10}^{-4}$.

Hence, option $\left(D\right)$ is correct.