Reflection of Sound

Introduction

Sound waves travel through a material medium. When a sound wave meets an obstacle, it does not always pass through it. Sometimes, it bounces back from the surface of the obstacle.

This bouncing back of sound from a surface is called the reflection of sound.

Reflection of sound is commonly observed when we hear an echo near a mountain, cliff, large wall or long corridor.

What is Reflection of Sound?

The bouncing back of sound waves from the surface of an obstacle is called reflection of sound.

Sound waves can reflect from obstacles such as solids and liquids. For example, sound can reflect from a wall, cliff, mountain, water surface or any large hard surface.

Reflection of Sound is Similar to Reflection of Light

Sound follows the same laws of reflection as light. When a sound wave falls on a reflecting surface, it is reflected back in a definite direction.

To understand reflection of sound, we use some important terms:

  • Incident sound wave: The sound wave that falls on the reflecting surface.
  • Reflected sound wave: The sound wave that returns after striking the surface.
  • Normal: A line drawn perpendicular to the reflecting surface at the point where sound strikes.
  • Angle of incidence: The angle between the incident sound wave and the normal.
  • Angle of reflection: The angle between the reflected sound wave and the normal.

Laws of Reflection of Sound

The laws of reflection of sound are:

  • The angle of incidence is equal to the angle of reflection.
  • The incident sound wave, reflected sound wave and the normal all lie in the same plane.

\(\angle i = \angle r\)

Diagram: Reflection of Sound

Reflection of Sound Reflecting Surface Normal Incident Sound Wave Reflected Sound Wave i r Source Listener Angle of incidence = Angle of reflection

Explanation of the Diagram

In the diagram, the sound wave falls on the reflecting surface. This wave is called the incident sound wave. After striking the surface, it comes back as the reflected sound wave.

The dotted line is the normal. It is perpendicular to the reflecting surface at the point of incidence. The angle made by the incident wave with the normal is equal to the angle made by the reflected wave with the normal.

Reflection from Different Surfaces

All surfaces do not reflect sound equally.

Type of Surface Effect on Sound Example
Hard and smooth surface Reflects sound strongly Wall, cliff, mountain surface
Soft surface Absorbs sound Curtains, upholstered chairs
Rough surface Scatters sound in different directions Uneven wall or rough surface

Examples of Reflection of Sound

  • When we shout near a mountain or cliff, the sound may reflect back to us.
  • In a long corridor, our voice may return after striking the walls.
  • In a large empty hall, sound reflects many times from the walls.
  • Hard and smooth walls reflect sound more clearly than soft surfaces.

Reflection of Sound and Echo

An echo is a common example of reflection of sound. If we shout near a large and distant reflecting surface, the sound reflects back and may be heard again after some time.

However, an echo is heard only when the reflected sound reaches our ears after a sufficient time gap. If the reflected sound returns too quickly, our brain cannot hear it as a separate sound.

Why Reflection of Sound is Important

Reflection of sound is useful in many ways. It helps us understand echoes, reverberation and the design of halls and auditoriums.

In large halls, sound reflection must be controlled properly. If sound reflects too much, it may become unclear. Soft and porous materials such as curtains and upholstered chairs help reduce unwanted reflections.

Important Terms

1. Reflection of Sound

The bouncing back of sound waves from the surface of an obstacle is called reflection of sound.

2. Reflecting Surface

The surface from which sound reflects is called the reflecting surface.

3. Incident Sound Wave

The sound wave that falls on a reflecting surface is called the incident sound wave.

4. Reflected Sound Wave

The sound wave that returns after reflection is called the reflected sound wave.

5. Normal

The line drawn perpendicular to the reflecting surface at the point of incidence is called the normal.

6. Angle of Incidence

The angle between the incident sound wave and the normal is called the angle of incidence.

7. Angle of Reflection

The angle between the reflected sound wave and the normal is called the angle of reflection.

8. Echo

The repetition of sound heard after reflection from a distant surface is called an echo.

Important Points

  • Sound waves can bounce back from obstacles.
  • The bouncing back of sound is called reflection of sound.
  • Sound can reflect from solids and liquids.
  • Sound follows the same laws of reflection as light.
  • The angle of incidence is equal to the angle of reflection.
  • The incident sound wave, reflected sound wave and normal lie in the same plane.
  • Hard and smooth surfaces reflect sound strongly.
  • Soft surfaces absorb sound.
  • Rough surfaces scatter sound in different directions.
  • Echo is a common example of reflection of sound.

Conclusion

Reflection of sound is the bouncing back of sound waves from a surface. Sound can reflect from obstacles such as walls, cliffs, mountains and water surfaces. Like light, sound follows the laws of reflection. The angle of incidence is equal to the angle of reflection, and the incident wave, reflected wave and normal lie in the same plane. Reflection of sound helps us understand echoes, reverberation and the proper design of halls and auditoriums.

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