This is a fundamental principle of reflection from a plane mirror. To see the full image of an object in a plane mirror, the minimum vertical extent of the mirror required is half the vertical extent of the object.Consider a person standing in front of a mirror. Light rays from the top of their head reflect off the top part of the mirror and enter their eyes. Light rays from their feet reflect off the bottom part of the mirror and enter their eyes. - The angle of incidence equals the angle of reflection. - The law of reflection dictates that to see the top of your head, the top edge of the mirror must be halfway between the top of your head and your eye level. - Similarly, to see your feet, the bottom edge of the mirror must be halfway between your feet and your eye level. - The distance between these two points on the mirror is the minimum required length. This distance is (1/2 distance from head to eye) + (1/2 distance from eye to feet). Since (distance from head to eye) + (distance from eye to feet) equals the total height of the person, the required mirror length is half the person's height.The distance of the person from the mirror does not affect the minimum length required, although it does affect the field of view.