A student focuses the image of a candle flame, placed at about 2 m from a convex lens of focal length 10 cm, on a screen. After that, he moves gradually the flame towards the lens and each time its image on the screen.
(a) In which direction does he move the lens to focus the flame on the screen?
(b) What happens to the size of the image of the flame formed on the screen ?
(c ) What difference is seen in the intensity (brightnees) of the image of the flame on the screen ?
(d) What is seen on the when the flame is very close (at about 5 cm) to the lens ?

Explanation

(a) When the flame is moved gradually towards the lens, u decreases. The screen has to be moved away from the lens.
(b) Size of image increases.
(c ) Intensity of image decreases.
(D) When size of image = size of object.
`|v|=|u| =2 f= 2 xx 10=20cm`