Question

The Focal Length Of Thin Convex Lens Is 20 Cm. When An Object Is Moved From A Distance Of 25 Cm Infront Of It To 50 Cm, The Magnification Of Its Image Changes From M25 To M50. The Ratio Of M25/ M50 Is ________

Answer 1

Answer:

Ratio of M25 : M50 = 3:1

Explanation:

When u = -25 cm

f = 20 cm

u = -25 cm

1/v - 1/u = 1/f

1/v = 1/f + 1/u

     = 1/20 - 1/25

     = 1/100

  v = 100 cm

M25 = v/u

        = 100/-25 = -4

When u = - 50 cm

1/v = 1/20 - 1/50

     = 3/100

  v = 100/3 cm

M50 = 100/ 3 x -25

        =  - 4/3

M25 /M50 =  4 x 4/3 = 3:1