Question

A boy focussed the image of candle flame on white screen using a convex lens .The position of candle is 26 cm. The position of convex lens is 50 cm. Position of screen is74cm. what is the focal length of convex lens and where will be image formed, if he shift candle towards lens at a position of 36 cm. Also draw ray diagram

Answer 1

U=50-26=24cm

V=74-50=24cm

So, f=12cm(since object distance=image distance)

When the candle is shifted towards the lens,

U=50-36=14cm.

The ray diagram is given below.

Answer 2

Answer:

( i ) .  Object distance u = 50 - 26 = 24 cm

Image distance v = 74 - 50 = 24 cm .

Since object distance is equal to image distance.

2 f = 24

= > f = 12 cm

So , focal length of object is 12 cm.

( ii ) . u = 50 - 38 = 12 cm

It's mean candle is at focus.

= > Image will form at infinity.

( ii ) Refer to attachment for ray diagram.