Step-by-Step Speed of Sound Experiment and Its Applications
The word “acoustic” is related to sound or the sense of hearing. It is a branch of sound that deals with understudies of mechanical waves in solids, liquids, and gases. These mechanical waves can be of sound, vibrations, ultrasound, and infrasound.
Since we are dealing with sound waves, so we will talk about Acoustic Sound. Sound travelling in the form of waves has some speed that can be in m/s, kmph, and mph.
Speed of sound is the distance travelled by a unit wave through the air/elastic medium carrying various units of measurement.
On this page, you will find multiple units of sound with the experiment to measure speed of sound in air.
Important Point:
In the 17th century, the French scientist and philosopher Pierre Gassendi is known to be the dist to attempt the measuring the speed of sound in air.
Speed of Sound in Air
For measuring the speed of sound, we need to measure the distance it covers through the medium.
For instance, the speed of sound in meters per second (in dry air) is 343 meters per second; however, this velocity value is considered at a temperature of 20 0C (68 0F).
Moving forward, the speed of sound is measurable in various media and units like we discussed for m/s (m/s = SI unit of speed).
Now, let’s discuss the speed of sound in miles per hour, speed of sound km per hour, and how the experiment for the determination of the speed of sound can be performed:
Speed of Sound in Various Units
The speed of sound is measured in the following units:
Speed of sound in Km per hour - 1,235 Kmph
Speed of Sound in miles per hour - 767 mph
Speed of sound in air feet per second - 1,125 ft s⁻¹
The velocity of sound is measured in hydrogen and oxygen (H2 and O2) is always 332 m/s.
Before starting with the experiment to measure the speed of sound, we must know the sound measurements symbols:
Measuring the Speed of Sound in Air
Point to Note:
The speed of sound strongly depends on the temperature and the medium through which it propagates.
Do You Know the Speed of Sound is Measured by Which Instrument?
We can measure the speed of sound by using an oscilloscope, a square-wave oscillator, and a piezo-electric pick-up.
A study of the connection between the space travelled, and therefore, the time of arrival of the sound wave allows a graphical determination of the speed of the heartbeat within the lucite rod.
Now, let us understand the experiment to measure speed of sound in air:
Experiment to Determine the Speed of Sound
Theory
In 1866, August Kundt first described this experiment. In this context, we will be performing a common experiment in physics. The acoustic tube is also known as the Kundt’s tube.
Aim of this Experiment:
This experiment aims to measure the speed of sound “c” in air, or other gasses, by observing standing acoustic waves in a tube.
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Do You Know?
We can determine the speed of sound in the air by using a smartphone and a cardboard tube.
However, for making the experiment economical/affordable in terms of equipment. We are measuring the speed of sound within 3% of the theoretical prediction.
Theory of the Experiment:
Now, start with the theoretical part:
We place the smartphone such the microphone is found within the opening of the tube. this is shown in the figure below:
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The phone is about to record audio with a frequency of 44.1 kHz. During the phone recording, the function generator app emits a pure wave.
The wave traverses a path from 50 Hz to 3000 Hz at a rate of 1 Hz s−1. The sound recording is stored in .wave format. This format makes for straightforward data analysis later.
For a sinusoidal wave with constant frequency f and wavelength, propagating in a medium, the speed of sound in the said medium is given by:
c = fλ
On determining the wave’s frequency and wavelength, we can measure the speed of sound in the medium.
When an acoustic wave enters through the open end of a half-closed tube and hits the closed-end, part of the wave is reflected towards the tube’s opened end. At specific wavelengths, the incident and the reflected wave form a standing wave.
In the antinodes of the standing wave, the points on the standing wave where the amplitude is maximum, the amplitude of the standing wave is greater than the amplitude of the incident wave.
The displacement antinode of the standing waves is the opening of the tube. The resonance wavelengths are the wavelengths at which the standing waves occur.
For the half-closed tube, the resonances occur when the tube’s length equals an odd number of quarter wavelengths of the incident wave:
λn = 4L/n,
Where
n = 1, 3, 5,....
Here,
“n” is the nth harmonic of the tube
L is the length of the tube.
The resonance frequencies fn of the tube, the frequencies at which standing waves occur in the tube, can be found by combining both equations:
λn = 4cL/n,
Where
n = 1, 3, 5,.....
Result:
Frequencies at peak amplitudes:
FAQs on How to Measure the Speed of Sound in Physics
1. What is the fundamental principle behind measuring the speed of sound?
The fundamental principle for measuring the speed of sound is based on the basic relationship between speed, distance, and time: Speed = Distance / Time. To measure it, you need to know the exact distance between the sound source and the observer and then accurately measure the time it takes for the sound to travel that distance. A common example is seeing a distant event (like a firework) and starting a timer, then stopping it when the sound arrives.
2. What is the formula to calculate the speed of sound in air, considering temperature changes?
The speed of sound in a gas is determined by its properties. The formula derived from Laplace's correction is v = √(γP/ρ), where γ is the adiabatic index, P is the pressure, and ρ is the density. However, a more practical formula relates the speed of sound in air directly to temperature:
v ≈ 331.5 + 0.6T m/s.
In this formula, 'v' is the speed of sound in meters per second, and 'T' is the air temperature in degrees Celsius. This shows that for every 1°C increase in temperature, the speed of sound increases by approximately 0.6 m/s.
3. Why does the speed of sound change with the temperature and the medium it travels through?
The speed of sound changes due to two main factors: the medium's properties and its temperature.
- Medium: Sound travels by causing vibrations in particles. In solids, particles are tightly packed and have strong intermolecular forces, allowing vibrations to pass very quickly. In liquids, particles are less tightly packed, and in gases, they are far apart. This is why sound travels fastest in solids, slower in liquids, and slowest in gases.
- Temperature: An increase in temperature raises the kinetic energy of the particles in a medium. This means they vibrate more readily and collide more frequently, enabling them to transmit the sound wave's energy more efficiently and at a higher speed.
4. How does the speed of sound in solids, liquids, and gases compare, and why is the difference so significant?
There is a significant difference in the speed of sound across different states of matter, following the general rule: Speed in Solids > Speed in Liquids > Speed in Gases.
The reason lies in the elasticity and density of the medium. Solids are highly elastic and dense, with molecules bound in a rigid lattice. This structure allows for extremely fast transmission of vibrational energy. Liquids are less compressible than gases, so the speed is intermediate. Gases have particles that are far apart and move randomly, making the transfer of energy much slower and less efficient.
5. What are some common experiments used in a physics lab to determine the speed of sound?
A classic laboratory method is the resonance tube experiment. This involves using a tuning fork of a known frequency over a column of air in a tube partially filled with water. The length of the air column is adjusted until resonance (a loud sound) is heard. By identifying the length at which this occurs, one can calculate the wavelength (λ) of the sound wave. Using the formula v = f × λ, where 'f' is the tuning fork's frequency, the speed of sound 'v' can be determined accurately.
6. What are some practical, real-world applications of measuring the speed of sound?
Measuring the speed of sound has several crucial real-world applications. Key examples include:
- SONAR (Sound Navigation and Ranging): Used in submarines and ships to map seabeds, detect underwater objects, and measure ocean depths by timing the echo of a sound pulse.
- Medical Ultrasonography: Medical imaging techniques use the reflection of high-frequency sound waves in the body to create images of organs and tissues. The speed of sound in different tissues is a critical factor.
- Architectural Acoustics: Engineers use knowledge of the speed of sound to design concert halls and auditoriums, ensuring sound travels clearly from the stage to the audience without undesirable echoes or dead spots.
7. Can the speed of sound be zero? Explain the physical limitations.
Yes, the speed of sound can be effectively zero under specific conditions. Sound is a mechanical wave, which means it requires a medium (particles) to travel. In a perfect vacuum, like outer space, there are no particles to vibrate and transmit the wave. Therefore, the speed of sound in a vacuum is zero. Theoretically, the speed would also approach zero at a temperature of absolute zero (0 Kelvin), as all molecular motion would cease, preventing the propagation of vibrations.
