Photograph of the ground are taken form an air-craft ,flying at an altitude of 2000 m by a camera with a lens of focal length `50 cm`. The size of the film in the camera is `18xx18cm`.What area of the ground can be photography by this camera at any one time.

Explanation

As here `u =-2000"m" "f", =0.50 "m"` , so from lens formula `(1)/(v) - (1)/(u) = (1)/(f)`,
we have `(1)/(v) - (1)/((-2000)) = (1)/(0.5) implies (1)/(v) = (1)/(0.5) - (1)/(2000)~=(1)/(0.5) ["as" (1)/(0.5)gt gt(1)/(2000)] implies v=0.5"m" = 50"cm" = f`
Now as in case of a lens , `m = (v)/(u) = (0.5)/(-2000) = -(1)/(4)xx 10^(-3)` So `I_(1)` = (ma)(mb) = `m^(2)A` `[because A= "ab"]`
`A = (I_(1))/(m^(2)) = (18"cm" xx 18"cm")/([(1//4) xx 10^(-3)]^(2)) = (720"m" xx 720"m")`