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Waves

The wave equation

  • 3 things to know
  • Paper 5

Overview

The equations v = f × λ and v = x ÷ t, calculating the speed, wavelength and frequency of water, sound, radio and light waves, and how wavelength changes when frequency doubles at a fixed speed.

What you need to know

Answer each one before you reveal it.

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Key term

State the equation linking wave speed, frequency and wavelength.

Key term

State the equation linking wave speed, distance and time.

Numbers

A water wave has a frequency of 5 Hz and a wavelength of 0.04 m. Calculate its speed.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    State the equation linking wave speed, frequency and wavelength.

    Model answer

    Wave speed = frequency × wavelength, or v = f × λ.

  2. 2

    State the equation linking wave speed, distance and time.

    Model answer

    Wave speed = distance ÷ time, or v = x ÷ t.

  3. 3

    A water wave has a frequency of 5 Hz and a wavelength of 0.04 m. Calculate its speed.

    Model answer

    Speed = 5 × 0.04 = 0.2 m/s.

  4. 4

    A sound wave of frequency 170 Hz travels at 340 m/s. Calculate its wavelength.

    Model answer

    Wavelength = 340 ÷ 170 = 2.0 m.

  5. 5

    A wave travelling at 12 m/s has a wavelength of 3.0 m. Calculate its frequency.

    Model answer

    Frequency = 12 ÷ 3.0 = 4.0 Hz.

  6. 6

    A pulse travels 850 m along a steel rail in 0.17 s. Calculate the speed of the pulse.

    Model answer

    Speed = 850 ÷ 0.17 = 5000 m/s.

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Key Concepts of Physics
Motion and Forces
Conservation of Energy
Waves

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2.5 × = 9000 s.
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ALength is measured in metres, with the symbol m.
BMass is measured in kilograms, symbol kg.
CTime is measured in seconds, symbol s.

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Watt means the unit of power, symbol W.
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