Question

A student focused the image of a candle flame on 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 screen = 88.0 cm

a) What is the focal length of the convex lens?

b) Where will the image be formed if he shifts the candle

towards the lens at a position of 31 cm?

c) Draw a ray diagram to show the formation of the image

in the case (b) as said above.

3

Sec​

Answer 1

Explanation:

Before shifting the candle,

u=12−50=−38cm 

v=88−50=38cm

f1=v1−u1

f1=381+381

f1=381+1

f=19 cm

Hence, before shifting the candle, it is placed at a distance of 2f from the mirror.

When candle is shifted towards the lens from this position, its distance from the lens is f<u<2f. In this scenario, image formed is virtual, diminished and erect.

Answer 2

Answer:

before shifting the candle,

u = 12 - 50 = -38cm

v = 88 - 50 = 38 cm

f1 = v1 - u1

f1 = 381 + 1

f = 19cm

hence, before shifting the candle ,it is placed at a distance of 2f from the mirror

when candle is shifted towards the lens from this position, it's distance from the lens is f<2<2f. in this scenario,imaged formed is virtual ,diminished and erect.