physics experiment - to verify the laws of reflection of sound
Answers
Aim
To verify the laws of reflection of sound.
Apparatus Required
One clock or watch with a quiet tick, two similar cylindrical hollow cardboard tubes of 30-50 cm length, rough or smooth sound reflecting surface, drawing board, white paper sheet, cardboard.
Theory
When a sound wave falls on an extended surface or obstacle of large size, it gets bounced back into the same medium but in different direction. This phenomenon is known as reflection of sound.
The laws of reflection for the sound waves are:
The angle of incidence made by the sound waves with the normal to the reflecting surface is equal to the angle of reflection in which sound waves get reflected, i.e.∠i = ∠r.
The incident sound wave, reflected wave and the normal at the point of incidence, all lie in the same plane.
Procedure
Fix a white plane paper on drawing board with the help of drawing pin at the four corners of white paper.
Draw a line XY along one edge of the paper. At any point P on this line, draw a normal PN.
Using protractor, make an incident angle of 30° with the normal PN and mark it as ∠APN.
Place a reflecting surface, such as stiff cardboard/plywood/glass slab/mirror on a line XY in upright position with the help of stand/modeling clay.
Place another cardboard along normal act as a screen. This does not allow the direct hearing of the ticking sound of the clock.
Arrange two cylindrical hollow cardboard tube in such a way that their open ends come close together as shown in the figure.
Keep a clock near the open end of the tube placed on the line AP.
Try to listen the clear and distinct ticking sound of the clock through the other tube placed on the other side of the screen by adjusting the position of the tube. Mark this position as B. Distinct sound can be heard because sound waves get reflected from the reflecting surface.
Lift the end B of pipe PB, vertically upward to a small height. Try to hear the sound of the table-clock now through the pipe PB.
Lift the tubes, reflecting surface and screen. Join the points B and P and measure the angle of reflection of sound wave.
Repeat the experiment by taking different values of angle of incidence and tabulate your observations.
Result
From the observations, we conclude that
within experimental error limit, angle of incidence is always/approximately equal to the angle of reflection.
the incident sound wave, reflected wave and the normal at the point of incidence all lie in the same plane. Hence the law of reflection of sound is verified.
Precautions
Reflecting surface and screen should be held vertically on the sheet of paper.
Position of the ticking clock should be along the axis of the hollow cylindrical tube placed along AP.
Mark the position of the second tube only when heard sound intensity of the ticking clock is maximum.
Ear, ticking clock and reflecting surface should be in the same plane.
Utmost care should be taken while taking the measurement of angle. The measurement of angle, either it is incident or reflection must be taken between the axis of the tube and the normal.