A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm. The power of the combination is

Options

A. `- 1.5 D`
B. `- 6.5 D`
C. `+ 6.5 D`
D. `+1.5 D`

Answer

A

Explanation

Focal length of the combination,
`(1)/(F)=(1)/(f_(1))+(1)/(f_(2))`
`rArr " " (1)/(F)=(1)/((+40))+(1)/((-25))`
`rArr " " F=-(200)/(3)cm`
As, Power, `P=(100)/(F)=(100)/((-200//3))=-1.5 D`