The diameter of the moon is `3.5 xx 10^3 km` and its distance from the earth is `3.8 xx 10^5 km`. It is viewed by a telescope which `10 cm`. Find the angle subtended at the eye by the final image.

Explanation

Here, `l = 3.5 xx 10^3 km = 3.5 xx 10^6 m`,
`r = 3.8 xx 10^5 km = 3.8 xx 10^8 m`
`f_0 = 4 m = 400 cm, f_e = 10 cm, beta = ?`
`m = (f_0)/(f_e) = (400)/(10) = 40`
Also, `m = (beta)/(prop)`
`:. beta - m prop = 40 xx ((l)/(r)) = 40 xx (3.5 xx 10^6)/(3.8 xx 10^8) rad`
=`36.84 xx 106-2 xx (180^@)/(pi) = 21.1^@`.