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Question

Choose the correct answer from the alternatives given.
Poynting vectors S is defined as S=1μ0E×B. the average value of Sover a single period 'T'is given by

A
E20/2cμo
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B
E20/cμo
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C
2E20/cμo
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D
E20/cμ2o
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Solution

The correct option is B E20/2cμo
Poynting vector is given by, S=E×Bμ0

Average value of magnitude of radiant flux density over one cycle is
Sav=1μ0E0×B0|(1T)T0cos2(kxωt)dt

[E=E0cos(kxωt),B=B0cos(kxωt)]

=E0B0μ0(1T)(T2)

=E0B02μ0 [T0cos2(kxωt)dt=T2]

Sav=E0(E0/c)2μ0=(12cμ0)E20 (B0=E0c)

So, option (A) is correct

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