Minimum area of the disc to collect all light

Classical Mechanics Level 2

A concave mirror of radius of curvature R R has a circular outline of radius r 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 < < R r << R .

The area of the disc has to be atleast __________ \text{\_\_\_\_\_\_\_\_\_\_ } .

π r 4 / R 2 \pi r^4/R^2 π r 5 / 4 R 3 \pi r^5/4R^3 π r 4 / 4 R 2 \pi r^4/4R^2 π r 6 / 4 R 4 \pi r^6/4R^4

Nikhil Murarka by nikhil murarka , 24, India

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1 solution

Upamanyu Mukharji
Oct 29, 2017

@Josh Silverman Sir, here what does circular outline mean? Could you show with a diagram please?

0 Helpful 0 Interesting 0 Brilliant 0 Confused

I imagine it's the area of the circle that forms the boundary of the mirror. E.g. the black rim around it in this photo But maybe @nikhil murarka can confirm?

Josh Silverman Staff - 3 years, 7 months ago

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