New
New
Year 10
OCR
Higher

# Using the wave speed equations

I can calculate the speed, frequency or wavelength of a wave using the wave equation.

New
New
Year 10
OCR
Higher

# Using the wave speed equations

I can calculate the speed, frequency or wavelength of a wave using the wave equation.

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## Lesson details

### Key learning points

1. The speed of wave can be caluated using wave speed = frequency × wavelength.
2. The speed of a wave can be caluated using wave speed = distance ÷ time.
3. The choice of equation to use to caluate wave speed depends on the information provided in the question.
4. Prefixes can be used with units to show very large or very small values.
5. The frequency of a wave does not change as it crosses a boundary from one wave medium into another.

### Common misconception

In, v = f × λ, speed is dependent on frequency and wavelength, rather then the medium.

Focus on speed being property of a medium and equation not being as an equation with three interdependent variables.

### Keywords

• Wave equation - wave speed = frequency × wavelength (v = f × λ)

• Wave speed - The speed of a wave through a medium. Given by the wave equation: wave speed = frequency × wavelength (v = f × λ)

• Frequency - The number of waves produced each second. Frequency is measured in Hertz (Hz)

• Wavelength - The distance between one wave crest (or trough) and the next is the wavelength of the wave.

• Prefix - A prefix is added to units to represent large or small values , for example 1 km = 1000 m and 1 mm = 0.001 m

Students whose mathematics skills are ready can be taught to rearrange the wave equation and speed equation instead of substituting in values at the start.
Teacher tip

### Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

## Starter quiz

### 6 Questions

Q1.
What is the name for the number of vibrations a wave makes in a second?
wavelength
amplitude
period
Q2.
What are the units for wave speed?
ms
s/m
m
s
Q3.
Which of these units cannot be used as a measure of wavelength?
cm
m
km
Q4.
What is an equivalent frequency of 330 000 Hz?
33 kHz
330 mHz
33 mHz
Q5.
A transverse wave and a longitudinal wave have the same speed. Which statement about the waves is correct?
Correct answer: If the frequency of each wave is the same, the wavelength will be the same.
The frequency of each wave is equal to the wavelength.
The transverse wave has a lower frequency than the longitudinal wave.
The transverse wave has a higher frequency than the longitudinal wave.
Q6.
Put these prefixes in order starting with the smallest.
1 - micro
2 - milli
3 - centi
4 - kilo

## Exit quiz

### 6 Questions

Q1.
Which of these can cause the speed of a wave to change?
Increasing the wavelength.
Decreasing the frequency.
Correct answer: Moving from one medium to another.
Increasing the amplitude.
Decreasing the amplitude.
Q2.
A wave has a wavelength of 1.5 m and a frequency of 5.0 Hz. What is its speed?
6.5 m/s
3.5 m/s
3.3 m/s
5.0 m/s
Q3.
A wave in a rope has a wavelength of 0.3 m, and it travels with a wave speed of 1.5 m/s. Calculate the frequency of the wave.
0.45 Hz
0.5 Hz
45 Hz
50 Hz
Q4.
A sound wave with a frequency of 150 Hz travels at 330 m/s in air. Calculate the wavelength of the wave.
0.45 m
180 m
2.2 cm
49.5 m
Q5.
Starting with the longest, put the waves in order of decreasing wavelength.
1 - λ = 0.40 km
2 - λ = 40 m
3 - λ = 0.40 m
4 - λ = 4.0 mm
5 - λ = 40 μm
6 - λ = 400 nm
Q6.
A wave has a wavelength of 60 mm and it travels with a wave speed of 3.0 km/s. Calculate the frequency of the wave.
50 mHz
50 Hz