A Galilean telescope is constructed by an objective of focal length 50 cm and a eyepiece of focal length 5.0 cm a. find the tube length and magnifying power when it is used to see n object at a large distancei normal adjustment b. if the telescope is to focus an object 2.0 m away from the objective what should be the tube length and angular magnification, the image again forming at infinity?

Explanation

f_0=500cm, f_e=-5cm`
a. `L=f_0-|f_e|(50-5)cm=45cm`
and `m=-f_0/f_e=50/5=10.`
`b. Using the equation `1/v-1/u=1/f` for the objective.
`1/v=1/f_0+1/u`
`=1/(50cm)+1/(-200cm)`
or v=66-67cm`
the tube length `L=v-|f_e-|=(66.67-5)cm`
or, L=61.67cm`
to calculate the angular magnification we assume that the object remains at large distance from the eye. In this case the angular magnification
`m=v/f_e=66.67/5=13.33.`
v is the distance of the first image from the objective which is subsituted for `f_0`.