Answer 1

Energy density in the electric field is `U_E = 1/2ε_0E^2`

Energy density in the magnetic field is `U_B = 1/(2μ_0)B^2`

We know E = Bc

`c = 1/sqrt(ε_0μ_0)`

`U_E = 1/2ε_0(cB)^2 = 1/2ε_0(1/(ε_0μ_0))B^2 = B^2/(2μ_0)`

now, `U_E = U_B`