Class 10 > Unit # 11: Sound > Factors that affect speed of sound in air

Explain two factors which affect the speed of sound.

1. Effect of Temperature

Temperature is also a condition that affects the speed of sound. Heat is a form of energy that depends upon the kinetic energy of molecules. Molecules of the medium at higher temperatures have more energy. Thus, they can vibrate at a higher rate. As the molecules vibrate faster, sound waves can travel more quickly. The speed of sound at room temperature (25°C) in the air is 346 meters per second. It is faster than 331 meters per second, which is the speed of sound in air at (0°C).

The formula to find the speed of sound at temperature T in the air is given as follows:

v = 331 × √(T / 273)

Here v is the speed of sound, and T is the absolute temperature of the air. This formula shows that the speed of sound in air increases with the increase in temperature.

2. Effect of Humidity

Humidity also affects the speed of sound in the air. The effect of water vapor on the speed of sound is minimum than that of dry air. The presence of moisture in air replaces oxygen and nitrogen gases that reduce the density of air because the molecular mass of water vapors (Molecular Mass = 18) is less than that of oxygen (Molecular Mass = 32) and nitrogen (Molecular Mass = 28) gases since the speed of sound in gases are inversely related to the square root of its density.

Thus, as humidity increases, the density of the air decreases and sound travels faster.