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Concave Mirror

A plane mirro...

Question

A plane mirror is placed 25 cm away from a concave spherical mirror perpendicularly on the principal axis (bottom of the plane mirror touches principal axis and the top is towards the vertical up) of the concave mirror. What should be the distance (in cm) in front of concave mirror, where we place a candle if its images formed after 1st reflection from plane mirror and then from concave mirror are at the same distances from the candle? The radius of the concave mirror is 40 cm.

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Solution

The image formed by the plane mirror must lie at the centre of curvature of the concave mirror, so that the image formed by the concave mirror must be formed at the same position (at the object position of the concave mirror.
Hence, x + 2 (25 –x) = R
x = 10 cm

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