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.

Options

A. `720 m xx 720 m`
B. `240 m xx 240 m`
C. `1080 m xx 1080 m`
D. `100 m xx 100 m`.

Answer

C

Explanation

As ground is at very large distance from camera, therefore image of ground can be assumed to be formed at the focus of the camera lens.
`:. v = 50 m = 0.5 m, u = -3 km = -3000 m`.
If `x` is length of ground photographed, then
`|m| = |h_i/(h_0)|=|(v)/(u)|`
or `(0.18)/(x) = (0.5)/(3000)`
`:. x = (3000 xx 0.18)/(0.5) = 1080 m`
`:.` Area of ground photographed `= 1080 m xx 1080 m`.