AQA · GCSE · Combined Science

    Course version: 8464 · Version from Sept 2018

    Properties of waves: frequency, f, in hertz, Hz

    Frequency, f, is the number of complete wave cycles passing a fixed point each second.

    Checked against the AQA 8464 specification (opens in a new tab) on .

    • Point 8 of 18
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Frequency, f, is the number of complete wave cycles passing a fixed point each second. It is measured in hertz, Hz, where 1 Hz equals one cycle per second. For example, if 20 crests pass a point in 4 s, then f = 20 ÷ 4 = 5 Hz. Frequency links to period by f = 1 ÷ T, so a wave with T = 0.2 s has f = 1 ÷ 0.2 = 5 Hz. On a displacement–time graph, frequency is the number of full cycles shown divided by the total time. Frequency is not the same as wave speed: a wave can have a high frequency but a long wavelength, and speed depends on both frequency and wavelength through v = f × λ.

    What earns the marks

    • States that frequency is the number of complete wave cycles per second.
    • Gives the unit of frequency as hertz, Hz, and uses it correctly in calculations.
    • Calculates frequency by dividing the number of cycles by the total time taken.
    • Uses the relationship f = 1 ÷ T correctly, including choosing the appropriate rearrangement.
    • Distinguishes frequency from wave speed and from wavelength when interpreting wave data.

    Common mistakes and how to put them right

    • Confusing frequency with period.

      Put it right: Frequency is cycles per second in Hz, while period is time per cycle in s.

    • Using f = T instead of f = 1 ÷ T.

      Put it right: f = 1 ÷ T, so a longer period gives a lower frequency.

    • Counting part cycles as whole cycles when finding frequency from a graph.

      Put it right: Count only complete cycles and divide by the total time for those cycles.

    Exam tips

    • Write the unit Hz after every frequency value, and remember that 1 Hz means one cycle per second.
    • When finding frequency from a graph, count complete cycles over a clearly stated time interval before dividing.
    • Check that frequency and period are reciprocals: if f increases, T must decrease, and their product f × T should equal 1.

    Try the lesson

    The start of the Properties of waves: frequency, f, in hertz, Hz lesson, made from checked teaching notes for this specification point.

    Have a go first

    A wave passes a point 20 times every second. What is the frequency of the wave?

    Listen

    Frequency, f, is the number of complete wave cycles passing a fixed point each second. It is measured in hertz, Hz, where 1 Hz equals one cycle per second. For example, if 20 crests pass a point in 4 s, then f = 20 ÷ 4 = 5 Hz. Frequency links to period by f = 1 ÷ T, so a wave with T = 0.2 s has f = 1 ÷ 0.2 = 5 Hz. On a displacement–time graph, frequency is the number of full cycles shown divided by the total time. Frequency is not the same as wave speed: a wave can have a high frequency but a long wavelength, and speed depends on both frequency and wavelength through v = f × λ. A strong answer earns marks for these points. States that frequency is the number of complete wave cycles per second. Gives the unit of frequency as hertz, Hz, and uses it correctly in calculations. Calculates frequency by dividing the number of cycles by the total time taken. Uses the relationship f = 1 ÷ T correctly, including choosing the appropriate rearrangement. A common slip: Confusing frequency with period: the error is treating Hz as seconds. Instead, frequency is cycles per second in Hz, while period is time per cycle in s. Exam tip: Write the unit Hz after every frequency value, and remember that 1 Hz means one cycle per second.

    See it

    A flowchart starting from the node Frequency, f. One branch leads to the definition: the number of complete wave cycles passing a fixed point each second. Another branch leads to the unit hertz, Hz, which leads to 1 Hz = one cycle per second. A further branch gives f = number of cycles ÷ total time. Another gives f = 1 ÷ T, which leads to longer period gives lower frequency. Two more branches state that frequency is not the same as wave speed and not the same as wavelength; the wave speed branch leads to speed depends on frequency and wavelength: v = f × λ.
    It shows what frequency is, its unit, how it is calculated from cycles and time or from period, and how it differs from wave speed and wavelength.

    Key words

    Say what each word means before you turn the card.

    Frequency

    Try answering aloud or in your head before turning the card.

    Hertz

    Try answering aloud or in your head before turning the card.

    Period

    Try answering aloud or in your head before turning the card.

    Wave speed

    Try answering aloud or in your head before turning the card.

    See every definition
    Frequency
    The number of complete wave cycles passing a fixed point each second, measured in hertz, Hz.
    Hertz
    The unit of frequency, where 1 Hz equals one cycle per second.
    Period
    The time per cycle in seconds, linked to frequency by f = 1 ÷ T.
    Wave speed
    A quantity that depends on both frequency and wavelength through v = f × λ, and is not the same as frequency.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A flowchart starting from the node Frequency, f. One branch leads to the definition: the number of complete wave cycles passing a fixed point each second. Another branch leads to the unit hertz, Hz, which leads to 1 Hz = one cycle per second. A further branch gives f = number of cycles ÷ total time. Another gives f = 1 ÷ T, which leads to longer period gives lower frequency. Two more branches state that frequency is not the same as wave speed and not the same as wavelength; the wave speed branch leads to speed depends on frequency and wavelength: v = f × λ.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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