Reflection of Light and Basic Terms Associated With It




Reflection: Bouncing back of a light ray after hitting a surface.
Incident ray: The light ray which strikes the surface.
Reflected ray: The light ray which returns from the surface after reflection.
Normal: An imaginary line perpendicular to the surface passing from the point of contact.
Angle of incidence: Angle between the incident ray and the normal
Angle of reflection : Angle between the reflected ray and the normal.


Laws of reflection

Laws of reflection states that:
  1. The incident ray, the reflected ray and the normal at the point of incidence all lie in the same plane. 
  2. Angle of incidence is equal to the angle of reflection. 


Verification of laws of reflection

Laws of verification can be experimentally verified by drawing the trace of a ray of light before and after reflection. This can be done by passing light through a small hole in a dark room or using two thin objects (like needles/pins) to trace a straight line and observe its reflection.


Image of point object formed by a plane mirror

The attached figure shows the formation of image (A') of a point object (A) by a plane mirror.


Verify the law of reflection

Aim : To verify the law of reflection


1) Take a drawing board and fix a white paper on it with the help of clamps.
2) Draw a straight line AB at the centre of the paper and also a normal (ON) to AB at point 'O'.
3) Draw a straight line PQ making certain angle (Angle i) with ON.
4) Fix two pins at the points P and Q on the paper vertically.
5)  Observe the image P' of the pin 'P' and 'Q' of the pin 'Q' in the mirror kept along the line AB.
6) Fix two more pins R and S such that they are in the same line as that of P' and Q'. Join RjS and 'O'.
7) Measure the angle between RS and ON (angle of reflection).
8) You will find that Angle of incidence = Angle of reflection
9) Repeat the experiment with different angles of incidence and measure the corresponding angles of reflection.
10)  In all cases you will observe Angle of incidence = Angle of reflection
11)  Hence 1st law of reflection is verified.


Image formation of point object by plane mirror

All light rays from the object when falls on a mirror, all corresponding reflected rays appear to come from a point behind the mirror which is called its image (virtual image).

The image formed is-
1. Of the same size of the object.
2. Is virtual and erect.
3. At the same distance behind the mirror as the object is kept in front of it.
4. It is laterally inverted. (Left appears right and right appears left).