The energy associated with electric field is ( U _ E ) and with...

The average energy density of electric field is given by

${u}_{E} = \dfrac{1}{2}ε{{E}_{0}}^{2}$

Here, ${E}_{0}$ is the maximum value of electric field.

The average energy density of magnetic field is given by

${u}_{B} = \dfrac{{{B}_{0}}^{2}}{2\mu}$

Here, ${B}_{0}$ is the maximum value of magnetic field.

The speed of light is given by ${c}^{2} = \dfrac{1}{\muε}$

Also, ${E}_{0} = c{B}_{0}$

So, ${u}_{E} = \dfrac{1}{2{c}^{2}\mu}{\left(c{B}_{0}\right)}^{2} = \dfrac{{{B}_{0}}^{2}}{2\mu} = {u}_{B}$

As the energy density of electric field and magnetic field are equal, the energy associated for equal volume will also be equal.