Objective lens of a telescope has focal length 100 cm. When the final image is formed at least distance of distance between the lenses is 105 cm. Calculate the focal length of eye piece.

Question

Objective lens of a telescope has focal length 100 cm. When the final image is formed at least distance of distance between the lenses is 105 cm. Calculate the focal length of eye piece. (A) 5 cm (B) 6.25 cm (C) 3 cm (D) 2 cm

Tardigrade Admin · Accepted Answer

L=f0+|ue| |ue|=L-f0=5 cm (1/ve)-(1/ue)=(1/fe) (1/- 25)-(1/- 5)=(1/fe) fe=6.25 cm

Q. Objective lens of a telescope has focal length $100 c m .$ When the final image is formed at least distance of distance between the lenses is $105 c m .$ Calculate the focal length of eye piece.

$5 c m$

$6.25 c m$

$3 c m$

$2 c m$

$L = f_{0} + ∣ u_{e} ∣$
$∣ u_{e} ∣ = L - f_{0} = 5 c m$
$\frac{1}{v _{e}} - \frac{1}{u _{e}} = \frac{1}{f _{e}}$
$\frac{1}{- 25} - \frac{1}{- 5} = \frac{1}{f _{e}}$
$f_{e} = 6.25 c m$

Q. Objective lens of a telescope has focal length 100cm. When the final image is formed at least distance of distance between the lenses is 105cm. Calculate the focal length of eye piece.

5cm

6.25cm

3cm

2cm