Question

Describe an activity to study the reflection of sound

Answer 1

To observe the reflection of sound, take a drawing board and fix it on the floor. Put two metallic or cardboard tubes as shown in Fig. These tubes are making some angle with each other. Put a clock near the end of one tube and a screen between the two tubes so that sound of clock may not be heard directly.

The sound (like tick-tick) waves pass through• the tube are reflected by the drawing board. The reflected sound waves enter the second tube and are heard by the ear placed in front of the second tube.

Answer 2

Aim -

To study the reflection of sound

Theory -

Sound is reflected following the same laws as followed by light rays. That is,the reflected ray lies in the same plane of incidence (in which the incident ray and normal to the reflecting surface at the point of incidence lies), and the angle of reflection (∠r) is equal to the angle of incidence (∠i ).

Material 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, you are required to hear very low-amplitude sound waves, it is therefore important to have a peaceful atmosphere. To hear such sounds clearly, it is further advised to put the fan off.

2. Using a chalk piece or a pencil, draw a line ON on the table

3. Now draw a line OC making an ∠i1 (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

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.

6. Keep the table-clock close to the open end Q of pipe PQ.

7. 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.

8. 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.

9. Measure ∠NOD. This is the angle of reflection (say ∠r1) for angle of incidence ∠i 1. Record observations.

10. 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.

11. Repeat step 2 onwards for three different values of angle of incidence ∠i and find the corresponding values of angle of reflection ∠r.

12. 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.

Observations-

Angle of reflection - 30°

Angle of incidence - 30°

Angle of reflection - 35°

Angle of incidence - 35°

Angle of reflection - 40°

Angle of incidence - 40°

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.