CBSE Class 12 · Geometrical OpticsShort Answer

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The image of a candle is formed by a convex lens on a screen. The lower half of the lens is painted black so as to be completely opaque. What will be the effect on the image formed?

Solution

Every part of a lens forms a complete image; rays from each point of the candle pass through \emph{all} parts of the lens and meet at the corresponding image point. Blackening the lower half only removes half the ray-bundle, so:

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Position and size of the image are \emph{unchanged} (still a full, inverted image on the screen).

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The \emph{intensity/brightness is halved}, since half the light-gathering area is blocked.

CBSE Class 12 Board · Subjective

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