JEE Main · 2023 · 01 Feb 2023 · Shift 2 · EM Waves

In an electromagnetic wave the energy is shared equally between the electric and magnetic fields, so the average electric energy density equals the average magnetic energy density, $⟨u_E⟩=⟨u_B⟩$. The total average energy density is their sum, $⟨u⟩=⟨u_E⟩+⟨u_B⟩=2⟨u_E⟩$. Hence $\frac{⟨u_E⟩}{⟨u⟩}=\frac{1}{2}$.