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تسجيل

To locate the Image of a Point

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  P-445

2025-12-16

524

To locate the Image of a Point. Let A (Fig. 1) be the point, the image of which is to be found. Since the angle of reflection is equal to the angle of incidence, the ray AB, perpendicular to the surface, will be reflected upon itself in the direction BA; and the image of the point A will be on BA or AB prolonged. Any other ray AC will be reflected as CE, making the angle of reflection ECD equal to the angle of incidence ACD; and the image will be on CE or EC prolonged. As the lines BA and CE are divergent in front of the mirror, their only point of intersection is at A', a point behind the mirror, which is the image of A. 

From the figure the triangles ABQ and A'RC are right triangles, and the line BC is common. The angles ACB and ECM' are equal, since ECD = ACD. _But A'CB also equals ECM'; hence the angle ACB equals the angle A'CB, and the triangles ABC and A'BC are equal in all their parts. Hence A'B = AB. This means that the image of a point in a plane mirror is on a perpendicular from the point to the mirror and as far behind the mirror as the object is in front of it.