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A concave mirror for face viewing has focal length of 0.4 m. The distance at which you hold the mirror from your face in order to see your image upright with a magnification of 5 is:

1. 0.24m
2. 1.60m
3. 0.32m
4. 0.16m

Correct answer: 0.32m

Solution

For an erect virtual image m=+5 in a concave mirror (f=-0.4 m): m=-v/u=+5 gives v=-5u. Using 1/v+1/u=1/f with u=-d: -4/(5d) = 1/(-0.4) -> 5d = 1.6 -> d = 0.32 m.

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