Question

A thin converging lens of focal length 10 cm is placed coaxially in contact with a thin diverging lens of focal length 15 cm. How will the combination behave? Justify your answer.

Answer 1

f₁ = 10 cm, f₂ = −15 cm

Focal length `1/f = 1/f_1 + 1/f_2`

= `1/10 - 1/15`

= `1/f = (15 - 10)/150`

= `5/150`

= `1/30`

f = 30 cm

The combination will behave as a converging lens of focal length f = 30 cm.