The plane faces of two identical plano-convex lenses each having a focal length of 50 cm are placed against each other to form a usual biconvex lens. The distance from this lens combination at which an object must be placed to obtain a real, inverted image which has the same size as the object is :

Options

A. 50 cm
B. 25 cm
C. 100 cm
D. 40 cm

Answer

A

Explanation

The focal length of the combination is
`" "1/F=1/f_(1)+1/f_(2)`
Given, `" "f_(1)=50cm, f_(2)=50cm`
`therefore" "1/F=1/50+1/50=2/50`
`rArr" "F=50/2=25cm`
Object when placed at centre of curvature forms a real, inverted image of same size as object `=(2 times 25=50 cm)`.