A plane EM wave travelling along z direction is described by E=Eosin(kz-wt)i and B=Bosin(kz-wt)j . show that

(i) The average energy density of the wave is given by Uav=1/4 ε o E o 2 +1/4Bo2/ μ o

(ii) The time averaged intensity of the wave is given by Iav=1/2c ε o E o 2

4 Views|Posted 7 months ago
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7 months ago

This is a long answer type question as classified in NCERT Exemplar

(i) UE= 1 2 ε o E 2

UB= 1 2 B 2 μ o

So total energy density = UE+ UB= 1 2 ε o E 2 + 1 2 B 2 μ o

E= Eo/ 2  and B=Bo/ 2

Uav= 1 4 ε o E 2 + 1 4 B 2 μ o

(ii) We know Eo=cBo and c = 1/ μ 0 ε 0

1 4 B 2 μ o = 1 4 E o 2 c 2 μ o = 1/4 ε o E o 2

UE= UB

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Physics Ncert Solutions Class 12th 2023

Physics Ncert Solutions Class 12th 2023

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