The electric field intensity of an electromag | vedclass

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Question

(D) For an electromagnetic wave propagating in free space,the intensity of the wave $I$ is proportional to the square of the electric field amplitude

Vedclass · Accepted Answer

inversely proportional

Vedclass · Answer

(D) For an electromagnetic wave propagating in free space,the intensity of the wave $I$ is proportional to the square of the electric field amplitude $E$ $(I \propto E^2)$.As the wave travels,the energy spreads over a spherical wavefront of area $A = 4\pi r^2$.Since intensity $I = \frac{P}{A} = \frac{P}{4\pi r^2}$,we have $I \propto \frac{1}{r^2}$.Equating the two relations: $E^2 \propto \frac{1}{r^2}$,which implies $E \propto \frac{1}{r}$.Therefore,the electric field intensity is inversely proportional to the distance $r$ traveled by the wave.

The electric field intensity of an electromagnetic wave is ....... to the distance it has traveled.

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