How is the working of telescope different

cbse
ray-optics

#1

How is the working of telescope different from
that of a microscope? The focal lengths of the objective and eyepiece of a microscope are 1.25 cm and 5 cm, respectively. Find the position of the object relative to the objective in order to obtain an angular magnification of 30 in normal adjustment.


#2

For microscope $f_{ o }$ = 1.25 cm, $f_{ e }$, = 5 cm
When final image forms at infinity, then magnification produced by eye lens is given by
m = -L/$f_{ o }$ . D/$f_{ e }$
=> - 30 =-L/1.25 x 25/5
=> L = 7.50 cm (l)
For objective lens, $v_{ o }$ = L = 7.5 cm, $f_{ o }$ = 1.25 cm Applying lens formula,

1/$f_{ o }$ = 1/ $v_{ o }$ - 1/ $u_{ o }$
1/1.25 = 1/7.5 -1/$u_{ o }$
$u_{ o }$ = -7.5 x 1.25 /6.25 = -1.5 cm

The object must be at a distance of 1.5 cm from objective lens.