Know that the speed of sound in air is approximately 330–350 m s⁻¹.
What is the Speed of Sound?
The speed of sound, denoted by \$v\$, is the distance travelled by a sound wave per unit time in a given medium. In air at room temperature (≈ 20 °C) the speed is roughly \$v \approx 330\text{–}350\ \text{m s}^{-1}\$.
Why Does the Speed \cdot ary?
Temperature:\$v\$ increases with temperature because the molecules move faster, reducing the time between collisions. Approximate relation: \$v \approx 331 + 0.6\,T\$, where \$T\$ is in °C.
Medium: Sound travels faster in solids and liquids than in gases because particles are closer together.
Humidity: More water vapour (lighter molecules) slightly increases \$v\$ in air.
Air Pressure: At a given temperature, pressure has little effect on \$v\$ because density and bulk modulus change proportionally.
Typical Speeds in Different Media
Medium
Speed of Sound (m s⁻¹)
Notes
Air (20 °C)
≈ 340
Range 330–350 m s⁻¹
Water (20 °C)
≈ 1480
Much higher due to greater rigidity
Steel
≈ 5000
Very high because of strong intermolecular forces
Measuring the Speed of Sound in Air
Set up two microphones a known distance \$d\$ apart (e.g., 2 m).
Produce a short, sharp sound (e.g., a clap) near the first microphone.
Record the time interval \$\Delta t\$ between the arrival of the sound at the first and second microphones using an oscilloscope or a digital timer.
Calculate the speed using \$v = \frac{d}{\Delta t}.\$
Repeat several times and take the average to reduce random errors.
Common Sources of Error
Inaccurate measurement of distance \$d\$.
Delay in the detection circuitry (trigger lag).
Temperature variations during the experiment.
Reflections causing secondary arrivals.
Example Calculation
Suppose \$d = 2.00\ \text{m}\$ and the measured time interval is \$\Delta t = 0.0059\ \text{s}\$. Then