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 = - 200 m f= 0.50 cm so from lens
formula `(1)/(v ) = (1)/(u) = (1)/(f) ` we have
`(1)/(v ) - (1)/((-2000)) = (1)/(0.5) rArr (1)/(v ) = (1)/(0.5) - (1)/(200) = (1)/(0.5)`
`[as .(1)/(0.5) gt gt (1)/(200)] 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 [ :. A = ab]`
i.e.,` A = (I_(1))/(m^(2)) (18 cm xx 18 cm)/([(1//4) xx 10^(-3)]^(2))`
`= (720 m xx 720m )`