What is the Law of Reflection of Light?
First law : The incident ray, the reflected ray and the normal at the point of incidence, all lie in the same plane.
Second law : The angle of reflection (∠r) is always equal to the angle of incidence (∠i).
i.e., ∠r = ∠i
(For normal incidence, i = 0, r = 0. The ray is reflected back along normal).
In figure the image of an object at A could be seen at A’ and the image of an object at B could be seen at B’, What conclusions can you draw from this observation? Look closely at the angle of incidence and the corresponding angles of reflection in figure. You will see that in each case, the angle of incidence (∠i) equals the angle of reflection (∠r). Also, the incident ray, the reflected ray, and the normal at the point of incidence lie on the same plane.
- 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 i.e., ∠i = 0. According to the law of reflection,
∠r = ∠i, ∴ ∠r = 0 i.e. the reflected ray is also perpendicular to the surface. Thus, an incident ray normal to the surface (i.e. perpendicular 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 as shown in figure (a) and (b).
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