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High School Physics

Reflection of Sound

Here, we will focus on the Reflection of Sound and find out important pointers about this incident. When sound waves strike a barrier and bounce back in the same medium, it is called the reflection of sound.

Reflection of Sound (Physics Notes)

  • Sound bounces off a solid or a liquid like a rubber ball bounces off a wall.
  • The sound gets reflected at the surface of a solid or liquid and follows the laws of reflection.
  • The angle of incidence is equal to the angle of reflection. This means, that the directions in which the sound is incident and is reflected make equal angles with the normal to the reflecting surface at the point of incidence, and the three are in the same plane.
  • An obstacle of large size which may be polished or rough is needed for the reflection of sound waves.

Laws of Reflection of Sound

The reflection of sound follows the laws of reflection of waves, which are:

  • The angle of incidence is equal to the angle of reflection.
  • The reflected sound, the incident sound, and the normal to the reflecting surface at the point of incidence belong in the same plane.

Applications of Reflection of Sound

The reflection of sound has many applications, some of which are:

  • Echo: Echo is the repetition of a sound caused by the reflection of sound waves. If the sound travels from a rigid surface, such as a cliff or a wall, then we can have the reflected sound with continuous vibrations.
  • SONAR: The Sound Navigation And Ranging technique uses the principle of reflection of sound to detect and navigate the objects available under the water.
  • Megaphone: Megaphones are like horn-shaped tubes that help to prevent echoes and multiple reflections while speaking.
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Examples of Reflection of Sound

Some examples of the reflection of sound are:

  • Reverberation: If the distance is less than 17 m, then the original sound mixes with the reflected sound. Due to repeated reflections at the reflecting surface, the sound gets prolonged. This effect is known as reverberation.
  • Echo: Echo is the repetition of sound created by the reflection of a sound wave.

Numerical Problem

Question: Suppose a man stands at a distance of 340 m from a cliff and claps his hands. He receives an echo from the cliff after 4 seconds. Calculate the distance of the cliff from the man.

Solution:

The time taken by the sound to travel from the man to the cliff and back is 4 seconds.

Therefore, the total distance traveled by the sound is twice the distance between the man and the cliff.

Let the distance between the man and the cliff be x.

Total distance traveled by the sound = 2x

Time taken by the sound to travel = 4 seconds

Speed of sound in air = 340 m/s

Using the formula, distance = speed x time,
we get: 2x = 340 x 4
=> 2x = 1360
=> x = 680 m
Therefore, the distance of the cliff from the man is 680 m

Solve more: Numerical problems based on sound (class 9)

Conclusion

The reflection of sound is a common phenomenon observed in our daily life. It follows the laws of reflection of waves and has many applications, such as SONAR, megaphones, and echoes. The distance of the reflecting surface can be calculated using the speed of sound and the time taken by the sound to travel.

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