A convex lens if in contact with concave lens. The magnitude of the ratio of their focal length is `(2)/(3)`. Their equivalent focal length is 30 cm. What are their individual focal lengths?

Options

A. `-75,50`
B. `-10,15`
C. `75,50`
D. `-15,10`

Answer

D

Explanation

`(f_(1))/(f_(2))=(2)/(3)`....(i)
`(1)/(f_(1))-(1)/(f_(2))=(1)/(30)` ...(ii)
Solving equation (i) and (ii)
`f_(2)=-15cm ( "Concave ")`
`f_(1)=10 cm ("Convex")`