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The magnetic field of a beam emerging f...

The magnetic field of a beam emerging from a filter facing a floodlight is given by `B=12xx10^-8sin(1.20xx10^7z-3.60xx10^14t)T`.
What is the average intensity of the beam?

A

`172 W m ^(-2)`

B

`1.72 W m ^(-2)`

C

`0.172 W m ^(-2)`

D

`17.2 W m ^(-2)`

Text Solution

Verified by Experts

The correct Answer is:
B
Given:
`B = 12 xx 10 ^(-8) sin (1. 20 xx 10 ^(7) z - 3. 6 xx 10 ^(15) t ) T`
Comparing with, `B = B _(0) sin (kz - omega t )`
`B _(0) = 12 xx 10 ^(-8) T`
` I _(av) = (c B _(0)^(2))/( 2 mu _(0)) = (( 3 xx 10 ^(-8)) xx (12 xx 10 ^(-8))^(2))/( 2 (4pi xx 10 ^(-7)))= 1. 72 W m ^(-2)`
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