d
(d)Intensity of \(EM\) wave is given by
\(I = \frac{P}{{4\pi {R^2}}} = {v_{av}}.c = \frac{1}{2}{\varepsilon _0}E_0^2 \times c\)
==> \({E_0} = \sqrt {\frac{P}{{2\pi {R^2}{\varepsilon _0}c}}} \)
\( = \sqrt {\frac{{800}}{{2 \times 3.14 \times {{(4)}^2} \times 8.85 \times {{10}^{ - 12}} \times 3 \times {{10}^8}}}} \)
\(= 54.77 \frac{V}{m}\)