Reflection of Sound

Like light, the sound reflects and obeys the laws of the reflection. Reflection of sound can be heard in long tunnels, deep wells, deep forest, deep ridges of mountains etc.

Echo is, simply, the reflection of sound by a hill or a large building some distance away. You can hear an echo only from a reflecting surface which is far away. This is because when sound reaches in your ears very quickly, your ears will not be able to distinguish it as a separate sound. In fact, your ears can able to distinguish two sounds as separate sounds only if the second sound wave is received 1/15th of a second or more after the first sound.The minimum distance for an echo to be heard is 17 m approximately.

Application of Echo

The principle of reflection of sound is used in an instrument called SONAR which is used to find the depth of the sea at any time. A SONAR produces ultrasonic pulses which are sent down into the sea from a ship. They are received back after being reflected by the bottom of the sea. SONAR stands for Sound Navigation And Ranging.

The depth of the sea is calculated by measuring the time taken by the echo to be received.

Nature also makes use of the principle of reflection of sound. The bat uses the echo to feel its way through and also to detect its prey. It gives out shrieks of ultrasound which gets reflected from any obstacle and avoids it. If echo comes from an insect, it easily recognises and catches it.

Absorption of sound

When sound falls on a surface, it is partly reflected and partly absorbed. Walls of aroom are good reflectors of sound. Wood, carpets, curtains, clothes and even our bodies absorb sound better and reflect less. In fact, soft surfaces are better absorbers of sound whereas hard surfaces are better reflectors of sound. Porous materials, Soft materials, non-metals, etc. are absorbers of sound.

Reverberations

If there are a number of reflecting surfaces near one another, a series of reflection takes place. Such sound is called reverberation. The reverberation of a thunder is due to thenumber of reflections of sound from clouds, rocks and cliffs, etc. Reflection of sound takes place in a big room, hall or newly constructed room. If the reflecting surface is less than 15m, reverberation distinguishes an echo from the source of a sound. The value of this suitable distance depends on the type of sound produced.