Question

A student-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 the lens as under Position of candle = 12.0 cm Position of convex lens = 50 cm Position of the screen = 88cm (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 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

Explanation:

given:

object distance=u=12-50--38cm

image distance =v=88-50-38cm

by using lens formula:

1)1/f=1/v-1/u

1/f=1/38+1/38=2/38

therefore, f=19cm

2) v?

if u-31-50=-19cm

f19cm

1/f=1/v-1/u

1/v=1/f+1/u

1/19-1/19

so, V=infinity, the image will be formed at

infinity as the object is kept at the focus.

3)As the object is shifted towards lens,

the object distances thus decreases and

so we would see a variation in image

nature,the image will be virtual,erect and

magnified.