1 \(\,\frac{{{B^2}}}{{2\lambda }}\)
2 \(\frac{{{B^2}}}{{2{\mu _0}}}\)
3 \(\frac{{2{B^2}}}{{{\mu _0}\lambda }}\)
4 \(\frac{B}{{{\mu _0}\lambda }}\)
Explanation:
Energy density of an electromagnetic wave,
\(\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,U = \frac{1}{2}{\varepsilon _0}{E^2} + \frac{1}{2}\frac{{{B^2}}}{{{\mu _0}}}\)
So, the magnetic energy density is
\(\frac{{{B^2}}}{{2{\mu _0}}}.\)