Question

Rohit focused the image of a candle flame on a white screen using a convex lens. He noted down the position of the candle, screen, and lens as under:
Postion of candle = 26 cm
Position of convex lens = 50cm
Position of screen = 74cm

1) what is the focal length of the convex
lens?
2) where will be the image be formed if
he shifts the candle towards the lens
a position of 38cm.

Answer 1

focal length of convex lens is 12 cm.
The image will be formed at infinty because the now in new position the object distance is equal to focal length of convex lens which means that object wiobjectplaced at principle focus.

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.