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 position of candle= 26.0cm
position of convex lens= 50.0cm
position of screen= 74.0cm

(1) what is the focal length of convex lens?
(2) where will the image be formed if the shifts the candle towards the lens at a position of 38cm ?
(3) draw ray diagram to show the formation of the image in case, as said above ?

Answer 1

1) focal length of lens is 12cm.
2)the image will be formed at infinity because the new position of object is 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.