Question

The magnifying power of the astronomical telescope for normal adjustment is $50$. The focal length of the eye piece is $2cm$. The required length of the telescope for normal adjustment is:

• A. $100cm$
• B. $98cm$
• C. $25cm$
• D. $102cm$

Answer 1

The correct option is D $102cm$

Magnification of telescope is given by, $M=\frac{f_o}{f_e}$

Hence, $f_o=50\times 2=100cm$

Length of the telescope, $L\approx f_o+f_e=102cm$