Question

Focal length of the objective of an astronomical telescope is 1m. Under normal adjustment, length of the telescope is 1.05 m. Calculate the focal length of the eyepiece

Answer 1

Given:

Objective's focal length,

fo = 1 m

Telescope's length,

L = 1.05 m

To find:

The focal length of an eyepiece,

fe = ?

Solution:

As we know,

For astronomical telescope, the formula will be:

⇒ $L = fo-fe$

On substituting the give values, we get

⇒ $1.05=fe+1$

On substracting "1" from both sides, we get

⇒ $1.05-1=fe+1-1$

⇒          $fe=0.05 \ cm$

Thus the focal length of an eye piece is "0.05 cm".