Question

In an electromagnetic wave the average energy density associated with a magnetic field will be:

• A. $\frac{1}{2}L{I}^2$
• B. $\frac{B^2}{2{\mu }_0}$
• C. $\frac{1}{2}{\mu }_0{B}^2$
• D. $\frac{1}{2}\frac{{\mu }_0}{B^2}$

Answer 1

The correct option is B $\frac{B^2}{2{\mu }_0}$

Energy density due to electric field=$\frac{1}{2}ϵE^2$

Energy density due to magnetic field=$\frac{1}{2}\frac{B^2}{\mu }$

Since $\frac{E}{B}=c=\frac{1}{\sqrt{ϵ\mu }}$

Energy density is equally contributed to by electric and magnetic fields.