CBSE Class 10 Science 2017 · Paper 31/1 · Question 36

Light - Reflection and Refraction 2 marks Medium

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 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 (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

The lens moves away from the screen; the image grows larger and dimmer; at 5 cm no image forms on the screen.

(A) He moves the lens away from the screen (towards the flame), because the image distance increases as the flame comes nearer. (B) The image of the flame becomes larger (and stays inverted). (C) The image becomes less bright (dimmer), because the light is spread over a bigger image. (D) No image of the flame is formed on the screen, at most a faint patch of light: with the flame inside the focal length the lens forms a virtual, erect, magnified image on the same side as the flame, which cannot be caught on a screen.

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CBSE Class 10 Science 2017 · Paper 31/1 · Question 36

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