Sound – Experiment, Viva Voce
EXPERIMENT
Aim
To verify the laws of reflection of sound.
Theory
1. Sound: It is a form of energy produced by vibration and it needs medium to
propagate.
2. Reflection of sound: As light reflects when it strikes any hard object (opaque),
sound also gets reflected when it strikes any object.
Laws of Reflection of sound
1. The angle of incidence is always equal to the angle of reflection.
2. The incident sound wave, the normal and the reflected sound wave lie in the same
plane.
Materials Required
Two highly polished metal tubes made up of stainless steel or aluminium of length 25
cm and diameter 2 cm, a drawing sheet, metal plate, a geometrical set, thumb pins,
drawing board/table, stopwatch, metal stand.
Procedure
1. Fix the white sheet on drawing board with thumb pin.
2. Draw a line AB to place the metal plate as reflecting surface with the help of metal
stand, and draw normal OP to this line as shown in the figure.
3. Now draw a line OC making an angle of 30° with the line OP.
4. Place one metal tube near to the point O of normal and metal plate on the line OC.
5. Place the ticking watch closer to one end of this metal tube.
6. Now place the second tube so that its one end is near to the point O. Bring your
ear close to the other end and adjust its position such that it collects the maximum
reflected sound.
7. Mark the position of the tube when it collects the clear and maximum reflected
sound.
8. Draw an extended line of reflected sound wave and mark it as OD.
9. Measure the angle of incidence and the angle of reflection.
10. Follow the above procedure and record your observation thrice.
Observation Table
Result
1. The angle of incidence is equal to the angle of reflection.
2. The incident, normal and reflected sound waves lie in the same plane.
Precautions
1. The metal plate should be placed vertical on the drawing board.
2. Both the pipes used should be clean and shining.
3. The sound producer i.e. stopwatch should be placed closer to the end of the
metallic tube.
4. Avoid touching of the source of sound to the metal tube.
5. Maintain complete silence in the lab.
VIVA VOCE
Question 1:
What produces sound?
Answer:
Vibration produces sound.
Question 2:
How do human beings produce sound?
Answer:
Due to the vibration of vocal cords.
Question 3:
Can sound travel through the vacuum?
Answer:
No.
Question 4:
What is the speed of sound in air?
Answer:
The speed of sound in air at 22° C temperature is 344 m/s.
Question 5:
What is reverberation?
Answer:
The repeated reflection of sound that results in the persistence of sound is called
reverberation.
Question 6:
How is the reverberation of sound reduced at home/auditorium?
Answer:
By using sound absorbing materials like curtains, draperies, ceiling with fibre boards
etc.
Question 7:
What is the audible range of sound for human beings?
Answer:
The audible range of sound is 20 Hz to 20,000 Hz.
