A ray of light will be reflected from a smooth surface in such a manner that the angle incident ray makes normal to the reflecting surface at the point of incidence which is precisely same as the angle that the ray which is reflected makes with normal. Also, the ray reflected along with the incident ray and the normal to the reflecting surface all lie on the same plane defined at the incident point and it shows θi=θr.
The ray model is very useful while studying the reflection of light, refraction of light and various images created by lenses, spherical mirrors and plane mirrors.
If the reflection takes place from a perfect plane surface, then we term it as regular reflection. The reflected light has a larger intensity in a particular direction and negligible intensity in all other directions.
If the reflection takes place from an irregular or rough surface the regular feature of light is not observed and although at every point the light ray gets reflected the overall effect observed is basically cancellation and overlapping of all reflected rays resulting in a diffused reflection.
Some Examples on Reflection and Ray Model of Light
Problem 1: Angle of incident for a plane mirror at the point of incidence is perceived to be 48 degrees with the normal. What is the angle of reflection?
(at the point of incident with normal) Angle of incidence = angle of reflection
Thus, angle of reflection = 48 degrees (with normal)
Problem 2: The angle of reflection with the normal at the point of incident is perceived to be 108 degrees. What is the angle of incidence?
Angle of incidence = angle of reflection
Thus, angle of incidence = 108 degrees (with normal)