Question

You are given two converging lenses of focal lengths 1.25 cm and 5cm to design a compaound microscope.if it is desired to have a magnification of 30, find out the separation between the object and the eyepiece.
or
A small telescope has an objective lens of focal length 150 cm and eyepiece of focal length 5 cm. What is the magnifying of the telescope for viewing distant objects on normal adjustment ?
If this telescope is used to view a 100 m tall tower 3 km away, what is the height of the image of the tower formed 3km away, what is the height of the image of the tower formed by the objective lens ?

Answer 1

Here, `f_0 = 1.25 cm, f_e = 5 cm`,
`d = 25 cm, L = ?, M = 30`
When final image is formed at the near point of eye, the magnifying power of compound microscope is given by
`M = (L)/(f_0)(1 + (d)/(f_e))`
`30 = (L)/(1.25) (1 + (25)/(5)) = (6 L)/(1.25)`
`L = (30 xx 1.25)/(6) = 6.25 cm`.