Question

A Galilean telescope has an objective of focal length $100\text{cm}$ and magnifying power $50$. The distance between the two lenses in normal adjustment will be -

• A. $75\text{cm}$
• B. $98\text{cm}$
• C. $55\text{cm}$
• D. $35\text{cm}$

Answer 1

The correct option is B $98\text{cm}$

Given:

$|f_0|=100\text{cm}$

$m=50$

We know that,

$m=\frac{|f_0|}{|f_e|}$

$\Rightarrow 50=\frac{100}{|f_e|}$

$\Rightarrow |f_e|=2\text{cm}$

Now, the length of Galilean telescope,

$l=|f_0|-|f_e|=100-2=98\text{cm}$

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