JEE Main2014PhysicsElectromagnetic WavesActual
During the propagation of electromagnetic wave in a particular medium :-
Options
- AElectric energy density is double of the magnetic energy density
- BElectric energy density is half of the magnetic energy density
- CElectric energy density is equal to the magnetic energy density
- DBoth electric and magnetic energy densities are zero
Correct answer
C. Electric energy density is equal to the magnetic energy density
Step-by-step solution
U V elec = 1 2 ∈ 0 E 2 ....(i) U V mag = 1 2 B 2 / μ 0 ....(ii) B = E C (for EMW) ....(iii) and C = 1 μ 0 ε 0 .....(iv) ∴ devide eq n (i) by (ii) ( U / V ) e l e c ( U / V ) m a g = 1 2 ε 0 E 2 1 2 B 2 / μ 0 = ( E B ) 2 μ 0 ε 0 by using eq (iii) & (iv) = C 2 C 2 = 1 ⇒ ( U / V ) e l e c . = ( U V ) m a g