Wavelength and Speed of Light in Different Materials

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To find out more about the diagram above . . . . read on!

Wavelength and Speed of Light in Different Materials

Look carefully at the diagram at the top of the page. Now check out the following questions (and answers)!

  1. Does the speed at which light travels change as it propagates through different transparent media?
  2. Give an example of a medium through which light travels more quickly?
  3. Are crown glass and diamonds fast media?
  4. Does the colour of a ray of light change as it travels through different media?
  5. Does the wavelength of a ray of light change as it travels through different media?

About the Diagram

Introducing the diagram! Read back and forward between the image at the top of the page and the explanation below!

This diagram shows the waveform of rays of red light (electromagnetic radiation) travelling through equally sized blocks of different transparent materials.

  • The top block contains a vacuum so the speed of light, the wavelength and the distance travelled are all shown to be 100%.
  • The diagram then illustrates the relative speed, wavelength and distance travelled as light passes through each of the other materials.
  • The speed of light in a vacuum is 299,792 kilometres per second. Different media reduce that speed by different amounts depending on their optical density.
    • Optically rare medium (air) = a faster medium  = smaller index of refraction.
    • Optically dense medium (glass) = a slower medium = larger index of refraction.
  • Notice that whilst the speed, wavelength and the distance travelled is different for each material, the frequency of the wave remains the same.
  • Remember that frequency involves counting the frequency with which oscillations of a wave pass a given point in a given amount of time.
  • In this diagram, there are seven wave-cycles in each case before each wave reaches the yellow line. The yellow line indicates the distance the light travels in each case over the same period of time. So the frequency is seven in every case.

Understanding the diagram:

  • The speed, wavelength and distance travelled by the wave decreases as it passes through the list of materials because the optical density (and so the index of refraction) of each material is progressively increasing.
  • Although the speed, wavelength and distance travelled by the wave decreases as it passes through each material, the number of waves generated over the same period of time remains the same.
  • Because the frequency remains constant the colour of the ray remains the same.

Follow the blue links for definitions . . . . or check the summaries of key terms below!

Some Key Terms

Move to the next level! Check out the following terms.

Colour

Things appear coloured to an observer because colour corresponds with a property of light that is visible to the human ...
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Electromagnetic spectrum

The electromagnetic spectrum includes electromagnetic waves with all possible wavelengths of electromagnetic radiation, ranging from low energy radio waves through ...
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Frequency

The frequency of electromagnetic radiation (light) refers to the number of wave-cycles of an electromagnetic wave that pass a given ...
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Medium

Any material through which an electromagnetic wave propagates (travels) is called a medium (plural media). In optics, a medium is ...
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Speed of light

The speed (or velocity) of a light wave is a measurement of how far it travels in a certain time ...
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Wavelength

Wavelength is a measurement from any point on the path of a wave to the same point on its next ...
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