## Speed of a Longitudinal Wave – Class 11 | Chapter – 15 | Physics Short Notes Series PDF for NEET & JEE

Speed of a Longitudinal Wave: The speed of a longitudinal wave, also known as the speed of sound, is the speed at which a disturbance travels through a medium. The speed of sound depends on the physical properties of the medium, such as the temperature, pressure, density, and elasticity.

## Speed of a Longitudinal Wave

In general, the speed of sound in a gas is proportional to the square root of the temperature and inversely proportional to the square root of the density. The speed of sound in a solid is proportional to the square root of the elastic modulus (stiffness) and inversely proportional to the square root of the density. The exact relationship between the speed of sound and the physical properties of the medium can be described by the following equation for a gas:

v = (γRT)1/2

where v is the speed of sound, γ is the ratio of specific heats, R is the gas constant, and T is the temperature.

For a solid, the speed of sound can be described by the following equation:

v = (Y /ρ)1/2

where v is the speed of sound, Y is the elastic modulus, and ρ is the density.

In conclusion, the speed of a longitudinal wave, or the speed of sound, depends on the physical properties of the medium, such as temperature, pressure, density, and elasticity. The speed of sound in a gas is proportional to the square root of the temperature and inversely proportional to the square root of the density, while the speed of sound in a solid is proportional to the square root of the elastic modulus and inversely proportional to the square root of the density.

## Examples of Speed of a Longitudinal Wave

An example of the speed of a longitudinal wave, or the speed of sound, can be seen in the propagation of sound through air. The speed of sound in air at room temperature (20°C) and atmospheric pressure (1 atm) is approximately 340 m/s. This means that if you clap your hands or make some other noise, the disturbance will travel through the air at a speed of 340 m/s.

The speed of sound in air can be affected by changes in temperature and pressure. For example, at higher temperatures, the speed of sound increases, while at lower temperatures, the speed of sound decreases. Similarly, at higher pressures, the speed of sound increases, while at lower pressures, the speed of sound decreases.

In conclusion, an example of the speed of a longitudinal wave, or the speed of sound, is the propagation of sound through air, which travels at a speed of approximately 340 m/s at room temperature and atmospheric pressure. The speed of sound in air can be affected by changes in temperature and pressure.

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