Question

An object viewed from a near point distance of 25 cm, using a microscopic lens with magnification '6', gives an unresolved image. A resolved image is observed at infinite distance with a total magnification double the earlier using an eyepiece along with the given lens and a tube of length 0.6 m, if the focal length of the eyepiece is equal to ______ cm.

Options

• 21

• 20

• 25

• 23

Answer 1

An object viewed from a near point distance of 25 cm, using a microscopic lens with magnification '6', gives an unresolved image. A resolved image is observed at infinite distance with a total magnification double the earlier using an eyepiece along with the given lens and a tube of length 0.6 m, if the focal length of the eyepiece is equal to 25 cm.

Explanation:

For simple microscope,

m = `1 + D/f_0`

`6 = 1 + 25/f_0`

`f_0 = 5` cm

For compound microscope,

m = `(LD)/(f_0f_e)`

`12 = (60 xx 25)/(5f_e)`

f_e = 25 cm.