AP EAMCET202125 Aug 2021Morning ShiftPhysicsElectromagnetic WavesActual
Which one of the following is the property of a monochromatic, plane electromagnetic wave in free space?
Options
- AElectric and magnetic fields have a phase difference of 2
- BThe energy contributions of both electric and magnetic fields are equal
- CThe direction of propagations is in the direction of B E
- DThe pressure exerted by the wave is the product of its speed and energy density
Correct answer
B. The energy contributions of both electric and magnetic fields are equal
Step-by-step solution
The average electric energy density of EM wave in free space, _E= 1 2 ₀ E^2 = 1 2 ₀ [ E₀ 2 ]^2 = 1 4 ₀ E₀^2...(i) Average magnetic energy density of EM wave in free space, aligned _B & = 1 2 ₀ B^2 2 = 1 2 ( B₀ 2 )^2 1 ₀ & = B₀^2 4 ₀ ...(ii)) aligned Using relation, E₀=c B₀= B₀ ₀ ₀ ...(iii) From Eqs. (i), (ii) and (iii), we get u_E=u_B Hence, energy contributions of both electric and magnetic fields are equal.