Definition and laws of Reflection of light.
When rays of light are incident on an opaque smooth polished surface , they are bounced back in the same medium . This phenomenon of bouncing back of rays of light in the same medium is called reflection of light.
Some useful terms associated with of reflection of light :
1. Point of incidence: The point on the reflecting surface at which a ray of light strikes at the time of reflection is known as the point of incidence . In above diagram , O is at the point of incidence.
2. Reflecting Surface : The reflecting surface is the surface from which the light is reflected . In the above diagram X'X is the reflecting Surface.
3. Normal : A perpendicular drawn on the reflecting surface at the point of incidence is called the normal. in above diagram , ON is the normal.
4. Reflected Ray : The ray of light reflected from the reflecting surface from the point of incidence is known as the reflected Ray , in the above diagram , OR is the Reflected ray.
5. Incident Ray : The light ray which strikes the reflecting surface at the point of incidence is known as the incident Ray , in the above diagram IO is the incident Ray.
6. Angle of Reflection : The angle that the reflected Ray makes with the normal is known as the angle of Reflection. It is represented by the symbol r. In the above diagram , ∠RON is the angle of reflection.
7. Angle of incidence : The angle that the incident Ray makes with the normal is known as the angle of incidence. It is represented by the symbol i . In the above diagram , ∠ION is the angle of incidence.
8. Plane of incidence : The plane in which the normal and the incident Ray lie is known as the plane of incidence. In the above diagram, the plane of the book page is the plane of incidence.
9. Plane of reflection : The plane in which the normal and the reflected Ray lie is known as the plane of reflection. In the above diagram , the plane of the book page , is the plane of reflection.
Laws of Reflection of Light :
First law of reflection:
The incident Ray , the reflected Ray and the normal to the reflecting surface all lie on the same plane.
Second law of Reflection:
The second law of reflection states that the angle of incidence is equal to the angle of Reflection.
∠i = ∠r
Special cases of Reflection of light :
A ray of light striking the surface normally retraces its path .
When a ray of light strikes a surface normally , then angle of incidence is zero. According to law of reflection, ∠r =∠i so ∠r=0 i.e, the reflected Ray is also perpendicular to the surface . Thus , an incident Ray normal to the surface retraces its path as shown in figure.
Laws of reflection are also obeyed when light is reflected from the spherical or curved surfaces .