Question

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 ?

Answer 1

(a) When the flame is moved gradually towards the lens, the lens has to be moved towards the flame.
(b) The size of image would increase.
(c ) The brightness of image of the flame on the screen would decreases.
(D) When `u =-5cm, f= 10cm`
`(1)/(v) = (1)/(f) + 1/u= 1/10 -(1)/(5)= (-1)/(10). v= -10 cm`
The image will be virtual. Nothing will be visible on the screen.