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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

`1.71 "W m"^(-2)`

B

`2.1"W m"^(-2)`

C

`3.2"W m"^(-2)`

D

`2.9"W m"^(-2)`

Text Solution

Verified by Experts

The correct Answer is:
A
Here,
`B = 12 xx 10^(-8) sin (1.20 xx 10^(7) z - 3.6 xx 10^(15) t)T`
Comparing it with, `B = B_(0) sin (kz - omega t)`,
we have `B_(0) = 12 xx 10^(-8)T`
`:. I_(av) = (1)/(2) (B_(0)^(2)c)/(mu_(0)) - (1)/(2) xx ((12 xx 10^(-8))^(2)xx3xx10^(8))/(4pixx10^(-7))`
`= 1.71 W m^(-2)`
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