Question

A reflecting telescope has a large mirror for its objective with radius of curvature equal to $80 \,cm$. The magnifying power of this telescope if eye piece used has a focal length of $1.6 \,cm$ is

• A. $100$
• B. $50$
• C. $25$
• D. $5$

Answer 1

Answer: (C)

$25$

Answer 2

The focal length of objective mirror $f_0 = \frac{R}{2}= \frac{80}{2}= 40\,cm$ and focal length of eye piece $= 1.6 \,cm$ $\therefore$ magnifying power, $m = \frac{f_0}{f_e}$ $= \frac{40}{1.6} = 25$