Cambridge IGCSE Physics 0625

Topic: 3.4 Sound

Objective: Know that the speed of sound in air is approximately 330-350 m/s

This section focuses on the speed at which sound travels through air. Understanding the speed of sound is crucial for explaining phenomena like echoes and the perception of sound in different environments.

Speed of Sound in Air

The speed of sound in air is not constant; it varies depending on factors such as temperature and humidity. However, under normal conditions, the approximate speed of sound in dry air at 20°C is 330 m/s. This speed increases with increasing temperature.

The range of speeds is typically given as 330-350 m/s. This variation is due to changes in air temperature and humidity.

Factors Affecting the Speed of Sound

• Temperature: The speed of sound increases with temperature. This is because the air molecules move faster at higher temperatures, allowing sound waves to propagate more quickly.
• Humidity: Humidity has a slight effect on the speed of sound. Higher humidity generally leads to a slightly higher speed of sound compared to dry air. This is because water vapor is less dense than dry air.

Speed of Sound in Different States

The speed of sound is significantly different in different states of matter:

State of Matter	Approximate Speed of Sound (m/s)
Solid	Much faster (e.g., 5000-50000 m/s)
Liquid	Faster than air (e.g., 1400-1500 m/s)
Gas	Slower than in liquids and solids (e.g., 330-350 m/s in air)

Formula for Speed of Sound (Ideal Conditions)

The speed of sound ($v$) in air can be approximated using the following formula:

$$v = 330 + 0.6 \times T$$

where T is the temperature in degrees Celsius.

This formula provides a reasonable estimate of the speed of sound for typical atmospheric conditions.

Real-World Implications

The speed of sound has important implications in various real-world scenarios:

• Echoes: The time it takes for sound to travel to an object and back determines whether we hear an echo.
• Musical Instruments: The speed of sound influences the pitch of musical notes.
• Sonar: Sonar systems use sound waves to detect objects underwater, relying on the speed of sound in water.