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i cant understand about incidence ray ,reflected ray,angle of incidence and reflection

In the given figure MM' is a plane mirror.The ray of light which falls on the mirror surface is called the incident ray.Here,AO is the incident ray of light.The incident ray gives the direction in which light falls on the mirror.The point at which the incident ray falls on the mirror is called the point of incidence.In the figure ,point O on the surface of the mirror is the point of incidence.We know that when a ray of light falls on a mirror.the mirror sends it back in another direction and we say that the mirror has reflected the ray of light.The ray of light which is sent back by the mirror is called the reflected ray.Here,OB is the reflected ray of light.The reflected ray of light shows the direction in which the light goes after reflection from the mirror. The 'normal' is a line at right angle to the mirror surface at the point of incidence. In other words, 'normal' is a line which is perpendicular to the mirror at the point of incidence. In the given figure, the mirror is MM' and the point of incidence is O. So, the line ON is the normal to the mirror surface at point O. The normal has been represented by a dotted line to distinguish it from the incident ray and the reflected ray.  Note that 'normal' is just a 'perpendicular line' to the mirror, and it should not be called the 'normal ray' like the incident ray or reflected ray. The normal is a line at right angles to the mirror surface. In other words, normal makes an angle of 90° with the surface of the plane mirror.

The angle of incidence is the angle made by the incident ray with the normal at the point of incidence. In other words, the angle between the incident ray and normal is called the angle of incidence. Here, the incident ray is AO and the normal is ON, so the angle AON is the angle of incidence. The angle of incidence is denoted by the letter i.

The angle of reflection is the angle made by the reflected ray with the normal at the point of incidence. In other words, the angle between the reflected ray and normal is called the angle of reflection. Here, the reflected ray is OB and the normal is ON, so the angle NOB is the angle of reflection. The angle of reflection is denoted by the letter r.