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Speed of Sound is the rate at which sound waves propagate across a medium. Speed of sound is defined as the distance traveled per unit of time by the point of a sound wave, such as compression or rarefaction. It remains constant for all frequencies in a given medium.
- Sound waves travel fastest in solids, followed by liquids, and then by gases.
- Speed of Sound in dry air at 20°C is 343 m/s.
- Sound waves travel more slowly at lower temperatures than high temperatures.
Speed of Sound in a given medium is calculated using the formula
| v = λf |
Here, v refers to the velocity, f is the frequency, and λ is the wavelength of the sound wave.
Read More: NCERT Solutions for Class 9 Science Sound
Key Terms: Speed of Sound, Wave, Wavelength, Frequency, Distance, Density, Temperature, Speed of Sound Formula, Solids
What is Speed of Sound?
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Speed of Sound is the dynamic propagation of waves taking place through different mediums.
- It varies depending on the medium in which it propagates.
- Speed of sound is unaffected by the frequency of the sound when it travels through a specific medium.
- It is affected by majorly two factors namely Density of the medium and Temperature of the medium.
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Speed of Sound Formula
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Speed of Sound is defined as the distance traveled by a sound wave in a given amount of time. Speed of Sound Formula is given as
| v = λf |
Where
- v refers to the velocity.
- λ refers to the wavelength of the sound wave.
- f refers to the frequency.
| Solved Example Example: How long will it take a sound wave with a frequency of 2 kHz and a wavelength of 35 cm to travel 1.5 kilometers? Solution: Speed of Sound Formula is given as: v = λ ν Substituting the values in the equation, we get v = 0.35 m × 2000 Hz = 700 m/s The time taken by the sound wave can be calculated as: Time = Distance Traveled/Velocity Substituting the values in the equation, we get Time = 1500 m/ 700 m/s = 2.1 s |
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Factors Affecting Speed of Sound
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Speed of sound is affected by the density and temperature of the medium through which it travels.
- Density of Medium: When the medium is dense, the molecules are packed tightly together, allowing sound to travel faster. As a result, as the density of the medium increases, the speed of sound also increases.
- Temperature of Medium: Temperature has a direct relationship with the speed of sound. As a result, the speed of sound increases as the temperature rises.
Speed of Sound in Different Medium
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The density and elasticity of the medium through which sound travels determine its speed. Sound travels fastest in solids than in liquids and gases. The faster sound travels through a medium, the greater the elasticity and the lower the density.
- Speed of Sound in Solids: Sound travels through solids by colliding with different molecules and particles. Solids have a higher density than other media, resulting in a fast speed of sound.
- Speed of Sound in Liquids: Liquids have a lower density than solids and a higher density than glasses. As a result, the speed of sound in liquids lies in between that of solids and gases.
- Speed of Sound in Gases: In gases, the speed of sound is independent of the medium. This is due to its consistency of gas density. The velocity of sound in gases is proportional to the square root of the absolute temperature in Kelvin.
- Speed of Sound in Vacuum: Because sound does not travel into a vacuum, its speed is zero. In a vacuum, there are no particles, thus this happens. Sound waves do not travel in vacuum.
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Things to Remember
- Speed of Sound is defined as distance travelled per unit of time by a sound wave.
- Sound travels at different speeds depending on the medium through which it travels.
- The speed of sound is highest in solids followed by liquids and gases.
- The higher the density of the medium, the faster the sound travels through it and vice versa.
- The higher the temperature, the faster the sound travels through any medium.
- Speed of Sound Formula is given as v = λf, where v is the velocity, λ is the wavelength, and f is the frequency.
Sample Questions
Ques. Define speed of sound. (2 Marks)
Ans. Speed of sound is defined as the rate at which sound waves propagate across a medium. The speed of sound is defined as the distance traveled per unit of time by the point of a sound wave. Under the same physical conditions, the speed of sound remains constant for all frequencies in a given medium.
Ques. What is Sound? (3 Marks)
Ans. Sound is a type of energy like heat and electricity. Sound is a vibration that travels through solid, liquid, and gas mediums as an acoustic wave and the medium exhibits contraction and expansion alternately.
Sound is also represented graphically as a series of continuous crests and troughs. The wavelength of a wave is the distance covered between two continuous crests and troughs. Frequency of sound is defined as the number of cycles covered per unit of time. Hertz is the unit of frequency of sound.
Ques. How long will it take a sound wave with a frequency of 4 kHz and a wavelength of 60 cm to travel 5 kilometers? (3 Marks)
Ans. Speed of Sound Formula is given as:
v = λ ν
Substituting the values in the equation, we get
v = 0.60 m × 4000 Hz = 2400 m/s
The time taken by the sound wave to travel a distance of 2 km can be calculated as follows:
Time = Distance Traveled/ Velocity
Substituting the values in the equation, we get
Time = 5000 m/ 2400 m/s = 2.08 s
Ques. Give a brief explanation about the speed of sound in solid. (3 Marks)
Ans. Sound is a disruption caused by particle collisions, such as one molecule colliding with another, and so on. Solids are denser than liquids or gases, which means that the molecules in solids are closer together than in liquids, and liquids are closer together than glasses. Because of their near proximity due to density, they can collide extremely rapidly. It takes less time for a solid molecule to collide with its neighboring molecule.
Speed of Sound in solids is 6000 meters per second, while steel has a sound speed of 5100 meters per second. Another fascinating fact about sound speed is that it travels 35 times quicker in diamonds than it does in air.
Ques. What is the Speed of Sound in Water? (3 Marks)
Ans. Liquids have a lower density than solids and a higher density than gases. As a result, the speed of sound in liquids lies in between the solids and glasses.
Sound travels faster in water than in air. In water, sound travels at a speed of 1480 meters per second. It's also worth noting that with distilled water, the speed can range from 1450 to 1498 meters per second. When the temperature is between 20oC and 25oC, the speed of saltwater is 1531 meters per second.
Ques. How long will it take a sound wave with a frequency of 0.8 kHz and a wavelength of 24 cm to travel 1.6 kilometers? (3 Marks)
Ans. Speed of Sound Formula is given as:
v = λ ν
Substituting the values in the equation, we get
v = 0.24 m × 800 Hz = 192 m/s
The time taken by the sound wave to travel a distance of 2 km can be calculated as follows:
Time = Distance Traveled/ Velocity
Substituting the values in the equation, we get
Time = 1600m/ 192 m/s = 8.33 s
Ques. Explain the speed of sound in Gases. (3 Marks)
Ans. Gases expand to cover a given space, thus, their density is largely uniform regardless of gas type, but solids and liquids are not. The square root of the absolute temperature determines the speed of sound in gases.
It is, however, unaffected by the frequency of the sound wave, as well as the pressure and density of the medium. However, none of the gases in real life are perfect gasses, and as a result, their properties vary significantly. At 20 degrees Celsius, the speed of sound in air is 343.2 meters per second, or 1,236 kilometers per hour.
Ques.What is Intensity of Sound? (2 Marks)
Ans. Intensity of sound is the amount of energy passing through per unit of area at that point. Intensity of Sound is inversely proportional to the square of the distance between the point and the source. It is directly proportional to the square of vibration and frequency and the density of the medium.
Ques. Give reason why the speed of sound maximum in solids. (1 Mark)
Ans. The speed of sound is maximum in solids as the molecules are tightly packed together, allowing sound waves to travel more quickly through it.
Ques. Define Sonic Boom. (1 Mark)
Ans. Sonic Boom is defined as an impulsive sound which is similar to the sound of thunder. Sonic Boom is produced by a body travelling faster than the speed of sound.
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