Subject: Science
A sound is a vibration that travels through the air or another medium and can be heard when they reach in a person's or animal's ear.The sound is produced by rapid to and fro movements, called vibrations. The sound travels through the air at a speed of about 332 meters per second.
Sound needs a medium to travel. The medium can be solid, liquid or gases. It cannot travel in a vacuum. Sound travels faster in solids and liquids than in gases. Sound travels at a speed of 1500 m/s in water and at 5000 m/s in steel. Sound travels roughly at a velocity of 330 m/s in the air at 00 Celsius. The velocity of sound is maximum in solid and least in gas. The sound is reflected from the hard surfaces. Soft surfaces are better on absorbing sound.
A sound wave is a periodic disturbance which travels through a medium transferring energy from one point to another without causing any permanent displacement of the medium. A sound wave is produced by vibrating bodies. The vibration causes the surrounding air molecules to vibrate also producing a disturbance of the air. This disturbance travels out from the source of vibration in the form of longitudinal waves, which is the sound you hear.
The number of complete waves sets up in a medium in one second is called frequency of the wave. Its SI unit is hertz (Hz).
The time taken by the wave to complete one cycle or a complete wave is called time period. Its unit is second.
The distance between two consecutive troughs or crests in a transverse wave or the distance between two consecutive compressions or rarefactions in a longitudinal wave is called wavelength. It is denoted by λ. If λ is the wavelength, f is the frequency and v is the propagation speed. Its SI unit is meter (m).
then,
The velocity with which sound wave propagates in a medium is called the velocity of a sound wave. Its SI unit is m/s. If λ is the wavelength, f is the frequency and v is the velocity of a sound wave.
then,
Transmission of sound:
The sound is produced by a vibrating body. It is propagated from the source to the listener through a medium in the form of sound waves. In the absence of a medium, no sound waves can travel.
Write any four sources of sound.
Any four sources of sound are bell, radio, guitar, and speaker.
Show by experiment that sound cannot travel in vacuum.
Let's put an electric bell in a bell jar and switch it on. At that time, we can listen the sound then take out all air from the jar using a vacuum pump. Again switch it on, but this time, we cannot listen the sound because sound needs a medium to travel. It cannot travel through a vacuum.
How can you say that sound travels through liquid?
A bell and a hammer is taken inside water. Firstly, bell is hammered when it is not touching the water. We hear a very weak sound but when the bell touches the water, we hear a louder sound. This shows that sound travels in liquid.
Find the velocity of a sound whose wavelength is 6.6 m and frequency is 100 Hz.
Solution
\begin{align*} \text {Frequency} = 100\: Hz \\ \text {wavelength} \: (\lambda ) = 6.6\: m \\ \text {velocity of sound}\:(v)\: =\: ? \\ V &= f \times \lambda \\ &= 100 \times 6.6 \\ &= 660 \: m/s \\ \therefore \text {velocity of sound is}\: 660\: m/s \\ \end{align*}
If the velocity of sound is 360 m/s and frequency is 100 Hz. Find the wavelength of the sound.
Solution
\begin{align*} \text {velocity of sound} \: (v) = 360\: m/s \\ \text {frequency} \: = 100\: Hz\\ \text {wavelength} \: (\lambda ) =\: ? \\ \text {according to formula} \\ V &= f \times \lambda \\ \text {or,} \: \lambda &= \frac vf \\ \lambda &= \frac {360}{100} \\ &= 3.6 m \\ \therefore \text {The wavelength of the sound is} \: 3.6 \: m. \\ \end{align*}
A gun is fired at a distance of 600 m from you. After how much time will you hear the sound? (speed of sound in air is 330m/s)
Solution
\begin{align*} \text {Distance travelled,}\:(s) = 600 m/s \\ \text {speed,}\: (v) = 330 m/s \\ \text {speed}\:(v) &= \frac {s}{t} = \frac {600\: m}{330\:m/s} \\ &= 2\: \text {seconds} \\ \end{align*}
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