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 focuses it's 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 (brightness) of the image of the flame on the screen ?
(d) What is seen on the screen when the flame is very close (at about 5 cm) to the lens ?

Answer 1

(a) He moves the lens away from the screen to focus the image.
(b) Size of the image increases.
(c) The intensity of image decreases as the flame moves towards the lens.
(d) Nothing can be seen as the image formed is virtual.