An astronomucal telescope has an eyepiece of focal-length `5 cm` If the angular magnification in normal adjustment is `10` , when final image is at least distance of distinct vision `(25cm)` from eye piece, then angular magnification will be :

Options

A. 10
B. 12
C. 50
D. 60

Explanation

For normal adjustment
`m=-(f_(0))/(f_(theta))`
when final image is at least distance of distinct vision from eyepiece, `m'=-(f_(0))/(f_(theta))(1+(f_(theta))/d)`
`=10(1+5/25) =12`