AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
Period = f requency T = f period, T, in seconds, s frequency, f, in hertz,…
Full specification wording
Properties of waves: period = f requency T = f period, T, in seconds, s frequency, f, in hertz, Hz The wave speed is the speed at which the energy is transferred (or the wave moves) through the medium.
Period and frequency are reciprocals: T = 1 ÷ f, with the period in seconds and the frequency in hertz.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 5 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Period and frequency are reciprocals: T = 1 ÷ f, with the period in seconds and the frequency in hertz. A 50 Hz wave has a period of 1 ÷ 50 = 0.02 s, and a wave with a period of 0.004 s has a frequency of 250 Hz. The period is read from a displacement-time graph as the time for one complete cycle. Wave speed is a different quantity: it is the speed at which the energy, or the wave itself, moves through the medium, measured in m/s, and it is found from wave speed = frequency × wavelength. Sound in air travels at about 330 m/s, while light travels at 3 × 10⁸ m/s. Period and wavelength are easily confused because both are read from a graph: the period comes from a displacement-time graph, the wavelength from a displacement-distance graph.
What earns the marks
- Writing period = 1 ÷ frequency.
- A correct substitution, such as T = 1 ÷ 50.
- The period given in seconds.
- Describing wave speed as the speed at which energy, or the wave, moves through the medium.
- Using wave speed = frequency × wavelength.
Common mistakes and how to put them right
Reading the printed formula as T = f and multiplying rather than taking the reciprocal.
Quoting a period in hertz or a frequency in seconds.
Using the speed of light in a calculation about a sound wave.
Dividing frequency by wavelength instead of multiplying when finding the wave speed.
Exam tips
- Write the reciprocal as a fraction on the page; it makes an inverted substitution obvious.
- Check the size of your answer: a period of many seconds implies a frequency well below 1 Hz.
- State which medium a speed applies to; wave speed changes from one medium to another.
Try the lesson
The start of the Properties of waves: period = f requency T = f period, T, in seconds, s frequency, f, in hertz, Hz The wave speed is the speed at which the energy is transferred (or the wave moves) through the medium. lesson, made from checked teaching notes for this specification point.
Have a go first
A loudspeaker produces a sound wave with a frequency of 50 Hz. What is the period of this sound wave?
Listen
Period and frequency are reciprocals: T = 1 ÷ f, with the period in seconds and the frequency in hertz. A 50 Hz wave has a period of 1 ÷ 50 = 0.02 s, and a wave with a period of 0.004 s has a frequency of 250 Hz. The period is read from a displacement-time graph as the time for one complete cycle. Wave speed is a different quantity: it is the speed at which the energy, or the wave itself, moves through the medium, measured in m/s, and it is found from wave speed = frequency × wavelength. Sound in air travels at about 330 m/s, while light travels at 3 × 10⁸ m/s. Period and wavelength are easily confused because both are read from a graph: the period comes from a displacement-time graph, the wavelength from a displacement-distance graph. A strong answer earns marks for these points. writing period = 1 ÷ frequency. a correct substitution, such as T = 1 ÷ 50. the period given in seconds. describing wave speed as the speed at which energy, or the wave, moves through the medium. Exam tip: Write the reciprocal as a fraction on the page; it makes an inverted substitution obvious.
See it
Key words
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period
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frequency
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reciprocal relationship
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wave speed
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See every definition
- period
- The time for one complete cycle, measured in seconds, s, and read from a displacement-time graph.
- frequency
- Measured in hertz, Hz, and related to the period as its reciprocal.
- reciprocal relationship
- Period and frequency are reciprocals: T = 1 ÷ f.
- wave speed
- The speed at which the energy is transferred (or the wave moves) through the medium.
Label the diagram
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