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Perfect Focusing Mirror

It is the yea...

Question

It is the year 932,320,228 AD, and our sun is now dying. Pranav, a young student of the ancient sciences stumbles upon a manuscript containing the design of a mirror, long lost to mankind. This design claims to be for the perfect focusing mirror, and Pranav hopes to put it to use to make the best of the invaluable sunlight. The mirror is

A

any concave mirror

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B

any convex mirror.

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C

a parabolic concave mirror.

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D

a plane mirror.

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Solution

The correct option is C a parabolic concave mirror.
Ok, so this was what the last video was about! If you apply Fermat's principle of least time to parallel rays falling on a general concave mirror, and require all the rays to pass through a common point, the focus (which makes it the perfect focusing mirror!), the profile you get for the mirror is parabolic. Go have a look again if it seems unclear how.

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