Question

A convex lens of power 3 D is held in contact with a concave lens of power -1D.A parallel beam of light is made to fall on the combination. At what distance from the combination will the beam get focussed?

Answer 1

Here, `P_1=3D,P_2= -1D, F=?`
`P=P_1 +P_2=(3-1)=2D`
`F=100/P = 100/2= 50cm`
`:.` The beam will get focussed at a distance of 50cm from the combination of lenses.