A student focused the image of a candle flame placed at 2 m from a convex lens of focal length 10cm, on a screen. After that he moves gradually the flame towards the lens and each time focuses its image on the screen

(A) In what 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 5cm) to the lens?

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Solution

(a)As the candle is moved towards the lens, the image distance increases. Thus, the student moves the lens away from the screen to focus the image. (b)The size of the image increases when the object is moved towards the lens. (c) Intensity decreases. (d) A virtual image is formed behind the candle on the same side of the screen

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