Question

Two point sources P and Q are 24cm apart. Where should a convex lens of focal length 9cm be placed in between them so that the images of both sources are formed at the same place?
A. 3cm fromP
B. 15cmfrom Q
C. 9cm from Q
D. 18 cm from P

Answer 1

Correct Answer - D
Let the image distance from lens be y

`1/y-1/-(24-x)=1/9`
`1/-y-1/-x=1/9`
`1/x+1/((24-x))=2/9`
`(24x-x^(2))/24 = 9/2`
`x^(2)-24x+108=0`
`x=6cm,18cm`