Question

An astronomical 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 (25 cm) from eye piece, then angular magnification will be :

• A. 10
• B. 12
• C. 50
• D. 60

Answer 1

The correct option is B 12

If $m$ is the magnification of a telescope in normal adjustment, then
$m^{\prime }=m(1+\frac{f_e}{D}$ )

Substituting the values,

$m^{\prime }=12$