Question

Two lens of power 3.5 d and -2.5d are placed in contact find focal length and power of the combination

Answer 1

Two lenses of power = 1.5 D and 3.5 D.

so, P1 + P2 = 3.5 + (-1.5)

= 3.5 - 1.5 = 2 D.

P = 1/f

2 = 1/f

2 = 100/f

2f = 100

f = 50 cm....

By lens formula 1/f = 1/v - 1/u...

we can calculate the image distance..

Answer 2

focal length=50cm.......