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Imaging and Signalling

Wave-forms, frequency and wave speed

  • 3 things to know
  • Components 01, 02 and 03

Overview

Recall questions on reading the period and amplitude from a wave-form, f = 1/T, v = fλ for radio waves and ultrasound, how wavelength limits the detail of an ultrasound scan, peak-to-peak voltage, and the wave-forms of pure and noisy signals.

What you need to know

Answer each one before you reveal it.

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Key term

State the relationship between frequency and period.

Numbers

A wave-form repeats every 20 μs. Calculate its frequency.

Numbers

A wave-form shows 4 complete cycles in 10 ms. Calculate the frequency.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What does the graph of a wave-form show?

    Model answer

    It shows how the displacement or voltage of a signal varies with time.

  2. 2

    How is the period of a signal read from its wave-form?

    Model answer

    It is the time for one complete cycle, measured between corresponding points on successive cycles.

  3. 3

    State the relationship between frequency and period.

    Model answer

    f = 1/T, with the frequency in hertz when the period is in seconds.

  4. 4

    A wave-form repeats every 20 μs. Calculate its frequency.

    Model answer

    f = 1/(20 × 10⁻⁶) = 5.0 × 10⁴ Hz.

  5. 5

    A wave-form shows 4 complete cycles in 10 ms. Calculate the frequency.

    Model answer

    One cycle takes 2.5 ms, so f = 1/(2.5 × 10⁻³) = 400 Hz.

  6. 6

    State the relationship linking the speed, frequency and wavelength of a wave.

    Model answer

    v = fλ, where v is the wave speed, f the frequency and λ the wavelength.

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