Question

The distance between the objective lens and the eye lens of an astronomical telescope, when adjusted for parallel light, is $100cm$. The measured value of the magnification is $19$. The focal length of the lenses are:

• A. $85$ cm and $25$ cm
• B. $82$ cm and $18$ cm
• C. $95$ cm and $5$ cm
• D. $50$ cm and $50$cm

Answer 1

Answer: (C)

$95$ cm and $5$ cm

$L=f_0+f_e$
$100=f_0+f_e$
$19=\frac{f_0}{f_e}$
$f_0=19f_e$
$\therefore f_0=95cm$
$f_e=5cm$