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A totally reflecting, small plane mirror...

A totally reflecting, small plane mirror placed horizontally faces a parallel beam of lighy as shown in figure. The mass of the mirror is 20g. Assume that there is no absorption in the lens and that 30% of the light emitted by the source goes through the lens. Find the power of the source needed to support the weight of the mirror. Take ` g= 10 m s^-2.

A

80

B

100

C

20

D

25

Text Solution

Verified by Experts

The correct Answer is:
B
For perfectly reflecting mirrorm, the force exerted by the light of power P is
`F = (2("power"))/(c )`
Power `=(mg xx c)/(2)=30xx10^(6)W`
As only 30 % of the power is given to the mirror
So, `P'=30xx(100)/(30)=100 MW`
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