Question

Two thin lens of power +3.5d and -1.5d Are placed in contact .find the combination of power of lens and focal length . If an object is placed at distance of 0.1m from lens combination where does the image formed?

Answer 1

Answer:

Given,

P1 = 3.5d

P2 = -1.5d

P = P1 + P2 = 3.5d + (- 1.5d)

= 3.5d - 1.5d = 2d

1/f = 1/v + 1/u

1/0.5 = 1/v + 1/0.1

1/v = 1/0.5 - 1/0.1

= 2 - 10 = -8

1/v = -8

v = 1/-8

Image distance is Negative. So, Image will form on the left side of Lens.

Answer 2

P = P1 + P2 = 3.5d + (- 1.5d)

= 3.5d - 1.5d = 2d

1/f = 1/v + 1/u

1/0.5 = 1/v + 1/0.1

1/v = 1/0.5 - 1/0.1

= 2 - 10 = -8

1/v = -8

v = 1/-8