Wavelength and frequency

Wavelength

Wavelength (symbol: $\lambda$ ) is defined as the distance from a point on one wave to the exact same (identical) point on the next consecutive wave.

It represents the length of one full cycle of a wave.
Wavelength is most commonly measured from one peak (crest) to the next adjacent peak, or from one trough to the next adjacent trough.
For longitudinal waves, such as sound waves, the wavelength is the distance between the centres of two consecutive compressions.
The standard unit for wavelength is metres (m).

Frequency

Frequency (symbol: $f$ ) is defined as the number of waves passing a given point per second.

It can also be defined as the number of complete oscillations or cycles occurring per second.
The standard unit for frequency is Hertz (Hz), where $1\text{ Hz}$ is equal to one oscillation per second.
The frequency of a wave is a property of the source. When a wave travels from one medium to another (for example, light moving from air into a glass block), the frequency remains constant, even though the speed and wavelength may change.

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Exam Tips

1
For OCR mark schemes, you MUST include 'per second' when defining frequency; simply writing 'the number of waves passing a point' will lose you the mark.
2
On a displacement-distance graph, students often confuse 'amplitude' and 'wavelength'. Remember that wavelength is measured along the horizontal (x) axis, while amplitude is measured on the vertical (y) axis.
Common Mistake
Wavelength $\lambda$ is measured in metres (m) and frequency $f$ is measured in Hertz (Hz) — never mix these up. When using the wave equation $v = f\lambda$ , always check that time is in seconds and distance is in metres before substituting.

Key Terms(9)

Wavelength: The distance from a point on one wave to the exact same identical point on the next consecutive wave (e.g., peak to peak).
Frequency: The number of waves passing a given point per second, or the number of complete oscillations per second.
Consecutive: Following continuously; in wave terminology, the very next adjacent wave cycle.
Hertz (Hz): The standard unit of frequency, equivalent to one complete wave cycle or oscillation per second.
Oscillation: One complete back-and-forth motion or cycle of a wave from its starting point and back again.
Compression: A region in a longitudinal wave where the particles are closest together.
Longitudinal waves: Waves in which the oscillations are parallel to the direction of energy transfer (e.g., sound waves).
Medium: The substance or material through which a wave travels (e.g., air, glass, water).
metres (m): The standard SI unit of length, used to measure wavelength.

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Key Terms(9)

Wavelength: The distance from a point on one wave to the exact same identical point on the next consecutive wave (e.g., peak to peak).
Frequency: The number of waves passing a given point per second, or the number of complete oscillations per second.
Consecutive: Following continuously; in wave terminology, the very next adjacent wave cycle.
Hertz (Hz): The standard unit of frequency, equivalent to one complete wave cycle or oscillation per second.
Oscillation: One complete back-and-forth motion or cycle of a wave from its starting point and back again.
Compression: A region in a longitudinal wave where the particles are closest together.
Longitudinal waves: Waves in which the oscillations are parallel to the direction of energy transfer (e.g., sound waves).
Medium: The substance or material through which a wave travels (e.g., air, glass, water).
metres (m): The standard SI unit of length, used to measure wavelength.

Wavelength and frequency

Wavelength

Wavelength (symbol: $\lambda$ ) is defined as the distance from a point on one wave to the exact same (identical) point on the next consecutive wave.

It represents the length of one full cycle of a wave.
Wavelength is most commonly measured from one peak (crest) to the next adjacent peak, or from one trough to the next adjacent trough.
For longitudinal waves, such as sound waves, the wavelength is the distance between the centres of two consecutive compressions.
The standard unit for wavelength is metres (m).

Frequency

Frequency (symbol: $f$ ) is defined as the number of waves passing a given point per second.

It can also be defined as the number of complete oscillations or cycles occurring per second.
The standard unit for frequency is Hertz (Hz), where $1\text{ Hz}$ is equal to one oscillation per second.
The frequency of a wave is a property of the source. When a wave travels from one medium to another (for example, light moving from air into a glass block), the frequency remains constant, even though the speed and wavelength may change.

Sign up to continue reading

Get full access to revision notes, key terms, and exam tips for every subtopic.

Exam Tips

1
For OCR mark schemes, you MUST include 'per second' when defining frequency; simply writing 'the number of waves passing a point' will lose you the mark.
2
On a displacement-distance graph, students often confuse 'amplitude' and 'wavelength'. Remember that wavelength is measured along the horizontal (x) axis, while amplitude is measured on the vertical (y) axis.
Common Mistake
Wavelength $\lambda$ is measured in metres (m) and frequency $f$ is measured in Hertz (Hz) — never mix these up. When using the wave equation $v = f\lambda$ , always check that time is in seconds and distance is in metres before substituting.

Key Terms(9)

Wavelength: The distance from a point on one wave to the exact same identical point on the next consecutive wave (e.g., peak to peak).
Frequency: The number of waves passing a given point per second, or the number of complete oscillations per second.
Consecutive: Following continuously; in wave terminology, the very next adjacent wave cycle.
Hertz (Hz): The standard unit of frequency, equivalent to one complete wave cycle or oscillation per second.
Oscillation: One complete back-and-forth motion or cycle of a wave from its starting point and back again.
Compression: A region in a longitudinal wave where the particles are closest together.
Longitudinal waves: Waves in which the oscillations are parallel to the direction of energy transfer (e.g., sound waves).
Medium: The substance or material through which a wave travels (e.g., air, glass, water).
metres (m): The standard SI unit of length, used to measure wavelength.

Previous Subtopic: Wave motion descriptionWave motion description Next Subtopic: Wave equationWave equation

Back to Wavelength and frequency

Put your knowledge into practice — try past paper questions for Physics A

Key Terms(9)

Wavelength: The distance from a point on one wave to the exact same identical point on the next consecutive wave (e.g., peak to peak).
Frequency: The number of waves passing a given point per second, or the number of complete oscillations per second.
Consecutive: Following continuously; in wave terminology, the very next adjacent wave cycle.
Hertz (Hz): The standard unit of frequency, equivalent to one complete wave cycle or oscillation per second.
Oscillation: One complete back-and-forth motion or cycle of a wave from its starting point and back again.
Compression: A region in a longitudinal wave where the particles are closest together.
Longitudinal waves: Waves in which the oscillations are parallel to the direction of energy transfer (e.g., sound waves).
Medium: The substance or material through which a wave travels (e.g., air, glass, water).
metres (m): The standard SI unit of length, used to measure wavelength.