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Minimum Height Of Plane Mirror Required For A Person To See Full Length Consider a person AB, such that A represents the highest point on his head, and B the lowest point on the foot such that E is the fixed eye level (see figure). The person will be able to see every part of his body if the can see points A and B. Let MN be the minimum length of mirror fixed on the wall, such that the rays AM and BN, after reflection, reach the eye of person, thereby forming an image A1B1 when produced backward.
In ∆AEA1, CM is parallel to AE and C is the mid-point of AA1. M is the mid-point of A1E.
Similarly, in ∆BEB1, ND is parallel to BE and D is the mid-point of BB1
∴ N in the mid-point of B1E.
Now in ∆A1B1E, M is mid-point of A1E and N is mid-point of B1E.
∴ MN is parallel and half of A1B1
But, A1B1 = ABSo, MN = 1/2 AB.
Thus, in order to see the full length, a person requires a plane mirror which is half his own height. This relation is true for any distance of the object from a plane mirror.