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Question
A student obtained a sharp image of a candle flame placed at the distant end of the laboratory table on a screen using a concave mirror to determine its focal length. The teacher suggested him to focus a distant building, about 1 km away from the laboratory, for getting more correct value of the focal length. In order to focus the distant building on the same screen, the student should slightly move the
(a) mirror away from the screen
(b) screen away from the mirror
(c) screen towards the mirror
(d) screen towards the building
Solution
In order to focus the distant building, which is 1 km from the laboratory, which means for the given concave mirror, the object (building) is at infinity, and to obtain the sharp building's image, the student should slightly move the screen towards the mirror.
Hence, the correct answer is option (c).
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