A telescope has an objective of focal length `30 cm` and an eye piece of focal length `3.0 cm`. It is focussed on a scale distant `2.0 m`. For seeing with relaxed aye, calculate the separation between the objective and eye piece.

Explanation

Here, `f_0 = 30 cm, f_e = -3.0 cm`,
`u_0 = -2.0 m = -200 cm`
`(1)/(v_0)=(1)/(f_0)+(1)/(u_0)=(1)/(30)-(1)/(200)=(17)/(600)`
`v_0 = (600)/(17) = 35.3 cm`.
For seeing the scale with relaxed eye, final image should be formed at infinity. This would happen when image formed by the objective lens lies at the focus of eye piece.
`:.` Distance between the objective and eye piece
=`v_0 + f_e = 35.3 + 3.0 = 38.3 cm`.