Question

When a telescope is adjusted for normal vision, the distance of the objective from the eye-piece is found to be $80cm$. The magnifying power of the telescope is $19$. What are the focal lengths of the lenses ?

• A. $61cm,19cm$
• B. $76cm,4cm$
• C. $40cm,40cm$
• D. $50cm,30cm$

Answer 1

The correct option is B $76cm,4cm$

As we know,

$f_o+f_e=80$ and $\frac{f_o}{f_e}=19\Rightarrow f_o=76$ and $f_e=4cm$.