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Lesson

Electromagnetic radiation

Electromagnet radiation is produced by the motion of electrically charged particles. Electromagnetic radiation is also called electromagnetic waves. Electromagnetic radiation can travel through space, air, water and other substances. Electromagnetic radiation acts like waves and also like a stream of particles called photons.

Radio waves, visible light, x-rays and so on are forms of electromagnetic waves. They all travel at approximately 300,000 kilometres per second through space. They have different wavelengths. The wavelength is the distance between the tops of successive waves.

The number of waves that passes fixed point in one second is the frequency. It is expressed in Hertz (cycles per second) which is abbreviated to Hz.

There is an indirect relationship between wavelength and frequency, expressed in the formula c = λ × f where c is speed of light, f is frequency of the wavelength and λ (Greek letter lambda) is the wavelength. Longer wavelengths have lower frequency and shorter wavelengths have higher frequency (when they are multiplied together the answer is always the same—300,000).

They also all travel in straight lines. This is an important issue for communications. Radio waves and microwaves are sent out from antennas. The receiving antenna must typically be in a line of sight with the broadcasting antenna. In some circumstances the atmosphere reflects broadcast signals back to earth. That's why you can sometimes pick up very distant AM stations on your radio. The curvature of the earth, high buildings and mountains all limit reception.

The electromagnetic spectrum

The electromagnetic spectrum is the complete set of wavelengths of electromagnetic radiation. Some of the common groupings are shown below. Radio waves, for example, range from about 1 cm to 1 km in wavelength.

For more information on how the electromagnetic spectrum works, go to

Be sure to follow the next page links to read the whole article, including:

  • Introduction to How the Radio Spectrum Works
  • Radio Frequencies
  • and Scanners

Activity

Assigned activities

Research and construct a detailed model of the electromagnetic spectrum. Include the following items on the drawing

  • the location of all major groups (i.e., radio)
  • the range of wavelengths in centimetres of all groups (i.e., radio is from 10 to 10-3 cm)
  • the frequency range in cycles per second (Hertz or Hz) of all groups (i.e., radio is everything less than 3 X 109

The model can be a drawing done on the computer in Corel Draw or some other tool, or by hand with colours and scanned. It can also be a computer animation.

The following is a list of starting points for research

Test Yourself

There is no self test for this lesson.