Experiment
Verification of laws of reflection
The following experiment can verify the laws of reflection.
A sheet of white paper is fixed on a drawing board, and a line MM 1, as shown below, is drawn. A point O is taken nearly at the middle of this line, and line OA is drawn such that ∠MOA is less than 90°. A normal ON is drawn on MM1 at the point O. A strip of plane mirror is set up vertically by using a stand with its silvered surface on MM1.
Now two pins, P and Q, are fixed vertically on the line OA, at some distance from the mirror on the board. Now keeping an eye on the other side of the normal (but on the same side of the mirror), the images of P and Q are seen. A pin R is fixed such that it is in line with the images of pins P and Q as observed in the mirror. Now one more pin S is fixed such that the pin S is in line with the pin R and the images of pins P and Q.
Small circles are drawn on the paper around the position of the pins. The pins are now removed. A line OB is drawn joining the pin–points S and R, which meet the mirror's surface at O.
AO is the incident ray OB is the reflected ray, ∠AON = i is the angle of incidence and ∠BON = r is the angle of reflection. The angles AON and BON are measured. It is found that the angle of incidence AON is equal to the angle of reflection BON.
The experiment is repeated with different directions of the incident ray AO. In each case, the angle of incidence and the angle of reflection are equal. This verifies the second law of reflection.
The experiment was performed on a flat drawing board, with the mirror normal to the board, and the lower tips of all the four pins lie in the same plane (i.e., the plane of the paper). This verifies the first law of reflection.