Example 11.2: Intensity of electromagnetic radiation

Question: Suppose that the intensity of the sunlight falling on the ground on a particular day is $140\,{\rm W}\,{\rm m}^{-2}$. What are the peak values of the electric and magnetic fields associated with the incident radiation?
 
Answer: According to Eq. (340), the peak electric field is given by

$$E_0 = \sqrt{\frac{2\,S}{\epsilon_0\,c}} = \sqrt{\frac{(2)\,(... ... 10^{-12})\,(3\times 10^8)}} = 324.7\,\,{\rm V}\,{\rm m}^{-1}.$$

Likewise, the peak magnetic field is given by

$$B_0 = \sqrt{\frac{2\,\mu_0\,S}{c}} = \sqrt{\frac{(2)\,(4\pi\... ...-7})\,(140)} {(3\times 10^8)}} = 1.083\times 10^{-6}\,{\rm T}.$$

Note, of course, that $B_0=E_0/c$.