To Verify the Laws of Reflection of Sound (Class 9 Physics Practical)
To demonstrate that sound follows the laws of reflection similar to light when it reflects off hard surfaces.
TL;DR: To demonstrate that sound follows the laws of reflection similar to light when it reflects off hard surfaces.
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Aim: To demonstrate that sound follows the laws of reflection similar to light when it reflects off hard surfaces.
Materials Required
- Two cardboard tubes or pipes
- Ticking clock or phone speaker
- Smooth hard wall or reflector
- Meter scale
- Protractor
- Stand/clamp
Theory
Sound waves reflect off hard surfaces following the laws of reflection: the angle of incidence equals the angle of reflection, and both lie in the same plane as the normal. The reflected sound can be heard clearly if the observer is positioned at the correct angle.
Procedure
- Place a ticking clock or speaker near the end of one cardboard tube (incident tube)
- Position the second cardboard tube (reflecting tube) such that it can receive the reflected sound
- Keep both tubes on either side of a hard vertical surface at equal angles to the normal
- Ensure the incident tube points toward the hard surface at an angle
- Listen through the reflecting tube to hear the reflected sound from the clock
- Measure the angle of incidence (angle between incident tube and normal)
- Measure the angle of reflection (angle between reflected tube and normal)
- Adjust the reflecting tube's position until maximum sound is heard
- Repeat with different angles of incidence
Observation
When the incident tube makes an angle with the normal, the reflected sound is clearly heard only when the reflecting tube is positioned at an equal angle on the opposite side of the normal. The intensity of sound is maximum when the angles are equal.
Result
The laws of reflection are verified for sound. The angle of incidence equals the angle of reflection in all cases, confirming that sound reflects following the same laws as light.
Precautions
- Use smooth, hard surfaces for better reflection
- Ensure both tubes are at the same height for fair comparison
- Measure angles from the normal perpendicular to the surface
- Use a consistent sound source throughout the experiment
- Avoid other sound reflections from nearby objects
Viva Questions
State the laws of reflection of sound.
The angle of incidence equals the angle of reflection, and both rays lie in the same plane as the normal.
How is reflection of sound different from refraction?
Reflection returns the sound back from the surface, while refraction would bend the sound when passing through different media.
Why does reflected sound have lower intensity than incident sound?
Some energy is absorbed by the surface, and some is dispersed in other directions, reducing the reflected sound intensity.
What type of surfaces are best for sound reflection?
Hard, smooth, solid surfaces like stone, glass, and metal are best for sound reflection.
More Class 9 Physics Practicals
- To Find the Focal Length of a Concave Mirror
- To Verify Ohm's Law
- To Find Resistance Using a Metre Bridge
- To Study the Laws of Reflection
- To Determine the Density of a Solid
- To Verify the Laws of Refraction (Glass Slab)
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