Wavelength & Speed of Light
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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.
Description
Wavelength & Speed of Light
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About the diagram
About the diagram
- 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 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.
Some key terms
Frequency
Medium
Electromagnetic spectrum
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