Question

Find the maximum and minimum magnifying powers of a telescope. Focal length of the lenses used are $12.5\text{cm}$ and $100\text{cm}$

• A. $10$ and $8$
• B. $12$ and $8$
• C. $18$ and $12$
• D. $22$ and $12$

Answer 1

The correct option is B $12$ and $8$

In a telescope, focal length of objective is larger than that of eyepiece.
So,
$f_0=100\text{cm}$ and $f_e=12.5\text{cm}$

$(MP{)}_{min}=\frac{f_o}{f_e}=\frac{100}{12.5}=8$

$(MP{)}_{max}=\frac{f_0}{f_e}(1+\frac{f_e}{D})$

$=\frac{100}{12.5}(1+\frac{12.5}{25})$

$\therefore (MP{)}_{max}=8\times \frac{3}{2}=12$

Hence, $\left(B\right)$ is the correct answer.