Question

Cl.
0.23. A student focussed the image of a candle flame on a white screen using a
convex lens. He noted down the position of the candle, screen and the lens as
under
Position of candle = 12.0 cm
Position of convex lens = 50.0 cm
Position of the screen = 88.0 cm
(i) What is the focal length of the convex lens?
(ii) Where will the image be formed if he shifts the candle towards the lens
at a position of 31.0 cm?
(iii) What will be the nature of the image formed if he further shifts the
candle towards the lens?
(iv) Draw a ray diagram to show the formation of the image in case (iii) as said
above.
​

Answer 1

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.