1.

The area of moon's image produced by a convex lens is proportional to focal length as :

Answer»

`sqrt(f)`
f
`f^(2)`
None of these.

Solution :(C ) `theta` be the angle subtended by RADIUS of moon at the OPTICAL centre of the lens

`tan theta = (r )/(f)` where r is radius of IMAGE of moon
`therefore r = theta f`.
AREA `= pi r^(2) = pi theta^(2) f^(2)`
`therefore "area" prop f^(2)`


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