Question

1. Two converging lenses, with focal lengths of f1 = 10.0 cm and f2 = 15.0 cm, respectively, are placed 40.0 cm apart. An object is placed 60.0 cm in front of the first lens.

   1. (a) Calculate the position, with respect to the second lens, of the final image formed by the combination of the two lenses.

   2. (b) Calculate the overall magnification of the final image formed by the combination of the two lenses.

Answer 1

Solution :-

Given data:-

f1 = 10 cm

f2 = 15 cm

u = 60 cm

(A) using lens formula for lens 1

1/f = 1/ v - 1/u

1/ 10 = 1/v + 1/ 60

v = 12 cm

Magnification, m1 = v/ u = 12 / 60 = - 0.2

Now the image formed by lens 1 acts as object for lens 2

u' = - ( 40 - 12) = - 28 cm

Using lens formula for lens 2

1/ f' = 1/ v' - 1/u'

1/ 15 = 1/v' + 1/28

v' = 32.308 cm tot he right of lens 2 ====>> Ans

(B) Magnificatio, m2 = v'/u' = - 32.308 / 28 = - 1.154

Net magnification

m = m1 * m2 = 1.154* 0.2 = 0.2307