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 = 26.0 cm Position of convex lens = 50.0 cm Position of screen = 74.0 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 38 cm? iii) Draw a ray diagram to show the formation of the image in case (ii) as said above?

Answer 1

heya it's Aastha!!!!!!

Given -
u = position of candle - position of lens 26-50=-24 .

v = position of screen - position of convex lens = 74-50 = 24 .

i) by using lens formula -------------------

1/f = 1/v- 1/u

1/f = 1/24-1/(-24)

1/f= 1/12

f = 12 cm .

ii) u = 50 - 38 = 12 cm

i.e. Candle is at f

So, image is formed at infinity.

hope it's clear to u !!!!!!!!

Answer 2

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 = 26.0 cm
Position of convex lens = 50.0 cm
Position of screen = 74.0 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 38 cm?
iii) Draw a ray diagram to show the formation of the image in case (ii) as said above?

1. u = 50 - 26 = 24 cm

v = 74 - 50 = 24 cm

2f = 24 cm

f = 24/2 = 12 cm

2. u = 50 - 38 = 12 cm

i.e. Candle is at f

So, image is formed at infinity.

3. i can't draw the image right here....