Question

Rohit focused the image of a candle flame on a white screen using a convex lens he noted down the positions of the candle screen and lens as under
Position of candle=26
position of convex lens=50
position of screen=74

Answer 1

distance of the image from the lens u=26-50 =-24cm
distance of the image from the lensv=74-50  24cm
to calculate the focal length the formula is
1/f=1/v-1/u
1/f=1/24+1/24
1/f=2/24 f=12cm
the object is placed at 2F1 and the image is formed at 2F2
so the image is of the same size as that of the object
the nature of the object is real and inverted  .

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.