# What is Sound | Sound Wave | Its Terms

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You might be thinking many times, What is sound?

Well we know, It is very difficult to conversate without sound, We also use sound for entertainment/enjoyment sound is a type of energy.

It is defined as that type of energy which is possessed due to vibration of bodies and can be reached experienced by our ears.

Let a plastic ruler vibrate by pressing it down the sound produces due to the vibration in the ruler. When a body moves to and fro about its mean position, it is to vibrate. So it’s obvious that,

Sound is produced due to the vibration of a body.

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## Sound wave

You know that sound can transmit through solid, liquid and gas medium.

In these mediums, the sound transmits in a special pattern of particles that is a longitudinal wave and this is what a wave is.

## 1. Amplitude

The maximal displacement of a vibrating body or particles from its mean position is called its amplitude.

It is found that the larger the amplitude, louder the sound.

For example, if a madal is struck gently, a soft sound is produced.

This is because the amplitude of vibration is less.

But, if it is hit hard, a loud sound is produced,

because the amplitude of the vibration is large. Its SI unit is metre (m).

## 2. Frequency

The number of complete vibrations made by a particle of a body in one second is its frequency. Its symbol is letter f. The SI unit of frequency is hertz (Hz).

For example, if a body makes 15 complete vibrations in one second, we say that its frequency is 15Hz. The larger unit of frequency is Kilohertz (kHz) and Megahertz (MHz).

1 Kilohertz (1 kHz) = 10^3Hz

1 Megahertz (1 MHz) =10^6 Hz

In the above diagram, 2.5 complete waves are produced in one second are shown,

Thus, the frequency of the wave is 2.5 Hz.

## 3. Time period

The time taken by a vibrating body to complete one vibration is called time period of that vibration.

Its symbol is T.

For example, the time period of a vibrating body is 2 seconds; it means, it takes 2 seconds to complete one vibration.

The SI unit of the time period is second (s).

## 4. Wavelength

The distance between two consecutive compressions or rarefactions of a sound wave is called wavelength of that wave.

Its symbol is A (lambda) and its SI unit is m.

For its clear concept see the diagram given above.

## 5. Speed of sound wave

The distance covered by a sound wave in one second is called speed of a sound wave.

It depends on the product of the wavelength and frequency of the wave.

Let the wavelength (A) of a sound wave by 0.25 m and its frequency (f) 1200 Hz It means that in one second 1200 complete waves are produced has wavelength 0.25

Now for the speed of sound

V =f x lambda = 1200 x 0.25 =300 m/s

Thus, the speed of sound is 300 m/s.

## Some solved numerical problems

### 1. In one second, 700 complete waves produce in a sound wave. If the wavelength of the wave is 0.46m, calculate the speed of the wave.

Solution:

Here, Wavelength (I) = 0.46 m

Frequency (f) = 700 Hz

Speed of sound (v) = ?

We have,

V = f × lambda(A)

= 700 × 0.46

= 322m/s

Thus, speed of the sound is 332m/s.

### 2. The speed of a sound wave in a steel rod is 7000 m/s and its wavelength is 0.16 m. Calculate the frequency of sound.

Given:

Here Speed of sound (v) = 7000 m/s

Wave length (A) = 0.16 m

frequency (f) = ?

We have,

V = f × lambda(A)

7000 =f x 0.16

f = 7000/0.16 = 43750 Hz

Thus, the frequency of the wave is 43750 Hz.

## Nature of sound

The main characteristics of sound are as given below:

(1) It shows the phenomenon like reflection and refraction as light does.

(2) It is a form of energy

(3) It travels in the form of a wave. A sound wave is a longitudinal wave.

(4) Sound requires a material medium (solid, liquid or gas) to travel. It cannot travel in a vacuum. The speed of sound is maximum in solid and minimum in gas.

## Speed of sound in different media

The speed of sound in unlike media is different.

It is more in solids and less in gases.

The speed of sound in some media is as given below:

## Medium – Speed (approx.)

Steel – 5000-7000 m/s

Wood – 4000-5000 m/s

Glass – 5000 m/s

Water – 1400 m/s

Alcohol – 1210 m/s

Air – 332 m/s

Hydrogen gas – 260 m/s

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