CIE IGCSE Physics

Revision Notes

3.1.1 Waves

Waves: Basics

  • Waves transfer energy between points, without transferring matter:
    • When a wave travels between two points, no matter actually travels with it: The points on the wave simply vibrate back and forth about fixed positions

 

  • The wavelength of a wave is the distance from a point on one wave to the same point on the next wave. Usually this is measured from the top of one wave to the top of the next wave
    Wavelength is usually measured in metres (a distance)
  • The amplitude of a wave is its height, measured from the middle of the wave to its top (or from the middle to its bottom)

 

amplitude-&-wavelength, IGCSE & GCSE Physics revision notesDiagram showing the amplitude and wavelength of a transverse wave

 

 

  • Wavefronts are a useful way of picturing waves from above: Each wavefront is used to represent a single wave

 

series-of-wavefronts, IGCSE & GCSE Physics revision notesDiagram showing a wave drawn as a series of wavefronts

 

  • The frequency of a wave is the number of waves passing a point (or being created or received) every second – it is helpful to think of it as being the waves per second
  • The units of frequency are hertz (Hz)

 

 

Exam Question: Waves

Exam Tip

When labelling wavelength on a diagram, make sure that your arrows go from the very top of a wave to the very top of the next one: if your arrow is too short you will lose marks.

Longitudinal & Transverse Waves

  • Waves can exist as one of two main types:
    • Transverse
    • Longitudinal

Transverse Waves

  • For a transverse wave, the points along the wave vibrate at 90 degrees to the direction in which the wave is moving (the direction of energy transfer)

 

Transverse wave definition, IGCSE & GCSE Physics revision notesWith a transverse wave, the vibrations are at 90 degrees to the direction of energy transfer

 

Longitudinal Waves

  • For a longitudinal wave, the points along the wave vibrate in the same direction that the wave is moving in

 

longitudinal-wave-definition, IGCSE & GCSE Physics revision notesWith a longitudinal wave, the vibrations are parallel to the direction of energy transfer

 

 

Exam Question: Longitudinal & Transverse Waves

Exam Tip

If asked to describe the difference between transverse and longitudinal waves, sketch the above diagrams. A good, clearly labelled diagram can earn you full marks.

Extended Only

The Wave Equation

  • The speed of a wave (v) is related to the frequency (f) and wavelength () by the equation:

Wave equation, IGCSE & GCSE Physics revision notes

  • You can rearrange this equation with the help of the formula triangle:

Wave speed triangle (2), IGCSE & GCSE Physics revision notesUse the formula triangle to help you rearrange the equation

 

 

Exam Question: The Wave Equation

Exam Tip

When stating equations make sure you use the right letters:
Eg. λ for wavelength, not L or W.

If you can’t remember the correct letters, then just state the word equations.

Be careful with units:

  • Wavelength is usually measured in metres and speed in m/s, but if the wavelength is given in cm you might have to give the speed in cm/s

Likewise, watch out for frequency given in kHz:

  • 1 kHz = 1000 Hz

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.
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