(a) An object 2 cm tall stands on the principal axis of a converging lens of focal length 8 cm. Find the position, nature and size of the image formed if the object is : (i) 12 cm from the lens (ii) 6 cm from the lens (b) State one practical application each of the use of such a lens with the object in position (i) and (ii).

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Solution

For the first case,

f = 8 cms
and u = − 12 cms

on substituting the values in the lens formula
1/f = 1/v − 1/u
1/8 = 1/v − 1/(−12)

v = 24 cms
It signifies the image to be bigger in size and inverted ,
with magnification factor -2
it will be real and of 4 cm

use:- can be used in film projector

In the second case the values in the lens formula
1/f = 1/v − 1/u
1/8 = 1/v − 1/(−6)

v = −24 cm Image is virtual and erect , larger in size , 8cms.

use:- can be used as magnifying glass

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