Question

An object is placed at a distance of 15cm from a convex lenx of focal length 10cm. On the other side of the lens, a convex mirror is placed at its focus such that the image formed by the combination coincides with the object itself. The focal length of the convex mirror is
A. `20cm`
B. `10cm`
C. `15cm`
D. `30cm`

Answer 1

Correct Answer - B

To refrance the path after reflection from mirror rays after refraction from lens must incident towards centre of curvature of mirror
Image by lens `(1)/(v)-(1)/(u)=(1)/(f) rArr (1)/(10+2f_(m))-(1)/(-15)=(1)/(10)`
`(1)/(10+2f_(m))=(1)/(10)-(1)/(15) rArr (1)/(10+2f_(m))=(3-2)/(30)`
`10+2f_(m)=30 rArr f_(m)=10cm`