An object is placed at a distance of 60 cm from a lens having focal length 30 cm. If a plane mirror is placed perpendicular to the principal axis of the lens and at a distance of 40 cm from it, the final image would be formed at a distance of:
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Question

An object is placed at a distance of 60 cm from a lens having focal length 30 cm. If a plane mirror is placed perpendicular to the principal axis of the lens and at a distance of 40 cm from it, the final image would be formed at a distance of:

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G1 Physics · Accepted Answer

Step 1: Lens first: u = −60 cm, f = +30 cm. By 1/v − 1/u = 1/f, v = +60 cm (first converging image). Step 2: Plane mirror at x = 40 cm reflects light. The converging point x = 60 cm (20 cm behind mirror) is mirrored to x = 20 cm in front of mirror. Rays then travel towards lens after converging through x = 20 cm. Step 3: At lens on return pass, these rays diverge as from a real object 20 cm to the right. With f = 30 cm, 1/v = 1/30 − 1/20 = −1/60, so virtual image lies 60 cm to right of lens. St…