Electromagnetic Waves

JEE Main level, single correct, medium

49 of 165

Question 49 of 165

The energy density associated with electric field E⃗\vec{E} and magnetic field B⃗\vec{B} of an electromagnetic wave in free space is given by (ϵ0−{\epsilon }_{0}- permittivity of free space, μ0−{\mu }_{0}- permeability of free space)

Show answer and solution

Answer: (B) UE=ϵ0E22,UB=B22μ0{U}_{E}=\dfrac{{\epsilon }_{0}{E}^{2}}{2},{U}_{B}=\dfrac{{B}^{2}}{2{\mu }_{0}}

When an electromagnetic wave propagates from the source, it transfers energy to the objects in its path. Electric and magnetic fields serve as energy reservoirs for electromagnetic waves. An electromagnetic wave contains the same amount of energy as are contained in the electric and magnetic fields together. In such situation, the energy density of the electromagnetic wave is equal to the sum of the energies of the electric and magnetic fields.
The average electric and magnetic energy densities are given by
UE=12ϵ0E2UB=12B2μ0\begin{matrix}{U}_{E} & = & \dfrac{1}{2}{\epsilon }_{0}{E}^{2} \\ {U}_{B} & = & \dfrac{1}{2}\dfrac{{B}^{2}}{{\mu }_{0}}\end{matrix}

JEE Main question paper PDF

Open a shift to read the full paper on this page, or download it.

JEE Main 2025 Apr 2 Shift 1 question paper

Open Download PDF

Opening paper…

Explain it as a whiteboard videoStep-by-step, in Hinglish or English. Your first video needs no login.Solved it on paper but got it wrong?Upload a photo of your working. Mistake Doctor marks the exact line that broke.

More Physics practice

JEE Main Physics practice question on Electromagnetic Waves (Electromagnetic Waves and Maxwell's equations), with the answer and a step-by-step solution. Scan a question from your own book or paper to get a whiteboard video.