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:
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mirror away from the screen
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screen away from the mirror
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screen towards the mirror
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screen towards the building
Solution
C.
screen towards the mirrorThe object, i.e., the distant building is at a distance of 1 km from the laboratory. That is, for the concave mirror, the building (object) is at infinity. In order to obtain a sharp image of the building, the student must slightly move the screen towards the mirror.
