Question

In an electromagnetic wave the average energy density is associated with:

• A. electric field only
• B. magnetic field only
• C. equally electric and magnetic fields
• D. average energy density zero

Answer 1

The correct option is C equally electric and magnetic fields

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.