Question

activity to show reflection of sound

Answer 1

AimTo verify laws of reflection of sound.

Materials Required
Two identical plastic pipes of length approximately 1 m and of diameter approximately 10 cm or less, a protractor (preferably of big size), a meter scale, and a source of low-amplitude sound such as a table-clock.

Procedure
1.⇒ In this experiment, very low-amplitude sound waves are heard so peaceful atmosphere is important. Fan is also off to hear the sound clearly.
2.⇒ Using a chalk piece or a pencil, draw a line ON on the table normal to the wall surface.
3.⇒Now draw a line OC making an ∠i 1 (say 30°) with the line ON.
4.⇒ Put one of the two plastic pipes (say PQ) along this line OC such that the end P of the plastic pipe is very close to point O on the wall. Now the axis of pipe PQ lies over the line OC (Fig. 44.2).
Step 5: Now put the second plastic pipe RS on the table, keeping its end R towards the wall on the other side of the normal ON. Mark the position of end R on the table.
5.⇒ Keep the table-clock close to the open end Q of pipe PQ.
6.⇒ Bring your ear close to the end S of pipe RS. Try to hear the sound of the table-clock through this pipe. Do you hear any sound? Keeping the position of the end R, adjust the position of pipe RS on the table to hear the sound of the table-clock. Mark the position of end S of the pipe RS where you hear the maximum sound.
7.⇒ Draw a line OD joining the point O on the wall, the point representing the position of end R, and the point representing the position of end S.
8.⇒Measure ∠NOD. This is the angle of reflection (say ∠r 1 ) for angle of incidence ∠i 1 . Record observations.
9.⇒ Keeping the position of the end R fixed, lift the end S of pipe RS vertically to a small height. Are you able to hear the sound of the table-clock through the pipe RS? If yes, lift end S pipe vertically to some more height. Do you still hear any sound? You will observe that on raising the height of end S, the sound of the table-clock either weakens or completely diminishes.
10.⇒Repeat step 2 on wards for three different values of angle of incidence ∠i and find the corresponding values of angle of reflection ∠r.
11.⇒ You might have drawn several lines on the table. As courtesy to the students coming to perform this experiment next, it is advised to remove all the lines drawn on the table.

Results :
1. The angle of reflection is equal to angle of incidence in all cases.
2. When the pipe through which the sound is heard, is lifted vertically the sound of the table-clock is either weakened or diminishes completely. It shows that the reflected ray lies in the same plane of incidence.
These observations verify that the sound reflects at the surface of a solid and follows the same laws of reflection as in case of light. In case if your observations are different from what are expected, discuss the reasons