Question

Rahul performs experiments with three convex lenses A, B and C of focal length 10 cm, 12 cm and 15 cm

respectively. He has done the experiments repeateally for three different values of object distances as 4 cm, 12 cm,and 18 cm. For which lens, he may get a magnification, = − 3?​

Answer 1

Answer:

none of the lenses, although the third lens will produce magnification of -5

Explanation:

MAGNIFICATION in lenses : v/u

according to lens formula: 1/f= 1/v -1/u

1/f + 1/u= 1/v

f+ u/ fu= 1/v

therefore, v= fu / f + u

replacing this in the magnification formula

v/u

= fu/ u(f + u)

now we will replace the different focal lenses and magnification

10 * 4/ 4( 10 +4)

40/ 4(14)

40/ 56  which is not equal to -3

now replacing f= 15 and u= - 18

15*18/ 18( 15 + (- 18))

270/ 18( -3)

 = -5

when focal length is 12 and object distance is twelve then image will be at infinity

v/u

infinity / 12 is not equal to 3