A light ray is coming from point A and is striking the plane mirror at point O. Point O is called as the point of incidence. Ray AO is called the incident ray. The angle made by AO with NO is called the angle of incidence . Angle of incidence is equal to the angle of reflection. A ray traveling along the normal NO is reflected back along NO itself.
Image is as far back from the mirror as the object is in front of the mirror.
The first four laws of reflection are easy to prove. Take a plane mirror, a sheet of paper and four pins. On the paper draw a line XY and place the mirror along it. XY represents the plane mirror. Keep the plane mirror edge along XY with its glass facing P 1 and P 2 .