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The minimum length of a plane mirror required for a person to view their full image does not need to be equal to their height. In fact, only half their height is sufficient due to the laws of reflection.
A mirror reflects light such that the angle of incidence equals the angle of reflection.
When a person stands upright in front of a mirror, rays from their feet and head reflect towards their eyes at equal angles.
Because of this, a 6-foot tall person only needs a 3-foot long mirror to see their entire image from head to toe.
The mirror does not need to be the same height as the observer because the mirror position, not its total size, determines the visibility of the image.
The top of the mirror should be aligned halfway between the observer's eyes and head, and the bottom of the mirror halfway between the observer's eyes and feet.
This works for any person regardless of height; a mirror half the person’s height is always enough to see the whole image.
This principle is used in mirror design for dressing rooms, vehicles, and optical instruments.
Saves material cost while still allowing full visibility.
6 feet or 12 feet: Not needed because of reflection geometry.
4 feet: More than necessary but still works.
None of these: Incorrect because a specific length exists.
A 6-feet tall person needs a 3-foot long mirror to view their entire image in a plane mirror (Option 4).
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