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A concave mirror of radius of curvature ...

A concave mirror of radius of curvature R has a circular outline of radius r. A circular disc is to be placed normal to the axis at the focus so that it collects all the light that is reflected from the mirror from a beam parallel to the axis. For r `gt gt R`, the area of this disc has to be at least

A

`(pi r^(6))/(4 R^(4))`

B

`(pi r^(4))/(4 R^(2))`

C

`(pi r^(5))/(4 R^(3))`

D

`(pi r^(4))/(R^(2))`

Text Solution

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The correct Answer is:
A
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    A
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