# Wave period and wave speed

The time period of a wave can be calculated using the equation:

This is when:

• time period (T) is measured in seconds (s)
• frequency (f) is measured in hertz (Hz)

### Example

Calculate the time period of a wave with a frequency of 5 Hz.

Question

Calculate the time period of a wave with a frequency of 400 Hz.

## Calculating wave speed

Wave velocity, the speed of a wave, can be calculated using the equation:

wave speed = frequency × wavelength

This is when:

• wave speed (T) is measured in metres per second (m/s)
• frequency (f) is measured in Hertz (Hz)
• wavelength (λ ) is measured in metres (m)

### Example calculation

What is the wave speed if the frequency is 50 Hz and the wavelength is 6 m?

Question

What is the speed of a wave with a frequency of 0.2 Hz and a wavelength of 25 m?

## The speed of sound in different materials

Sound is a mechanical longitudinal wave. The wave is passed on by collisions between particles, so the speed the wave moves depends on the density of the particles.

MediumStateSpeed of sound
SteelSolid6,000 m/s
WaterLiquid1,500 m/s
AirGas330 m/s

When sound moves from one into another, the change in speed will also cause a change in wavelength, frequency is unaffected.

wave speed = frequency × wavelength

Constant frequency means that the wavelength will be proportional to the wave velocity.