Question

4.
A point source of light is placed at a distance of 2f from a converging lens of focal length f. The intensity
of the other side of the lens is maximum at a distance of
a) f
b) between fand 2f and 2f
c)2f d) morethan 2f​

Answer 1

Answer:

For object placed at center of curvature of lens, image is formed at center of curvature on other side of the lens.

Hence, CE=2f

Since, final refracted rays are parallel to the axis, rays are coming from focus of the lens.

CD=f

DE=CE−CD=2f−f=f

Using laws of reflection, OD=OE

OD+OE=DE

⟹OD=DE/2=f/2

d=CD+DO=f+f/2=3f/2

d=3×30/2=45 cm