Question

Find the magnifying power of the telescope in case of normal adjustment, if the length of the telescope and focal length of the eyepiece is $38\text{cm}$ and $2\text{cm}$ respectively?

• A. $40$
• B. $20$
• C. $18$
• D. $22$

Answer 1

The correct option is B $20$

Given,

Length of telescope, $L=38\text{cm}$

Focal length of eyepiece, $|f_e|=2\text{cm}$

We know, in case of normal adjustment
$L=f_o-|f_e|$

$\Rightarrow 38=f_o-2$

$\therefore f_o=40\text{cm}$

Now, magnifying power,

$m=\left|\frac{f_o}{f_e}\right|=\frac{40}{2}=20$

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