Physics Notes

Page 1 of 3

Physics Notes

By | April 2013
Page 1 of 3
3. Recent technological developments have allowed greater use of the electromagnetic spectrum
1. describe electromagnetic waves in terms of their speed in space and their lack of requirement of a medium for propagation In space (a vacuum) electromagnetic waves travel at the speed of light, a constant equal to 3.00108ms1. Unlike sound waves, electromagnetic waves do not vibrate particles, therefore they do not need a medium (substance) to propagate (move). 2. identify the electromagnetic wavebands filtered out by the atmosphere, especially UV, X- rays and gamma rays The electromagnetic spectrum is spit up by varying wavelengths, long wavelengths are radio waves, and short ones are gamma rays. This is shown in the diagram below. Fig. (4)

The EMR (Electromagnetic Spectrum)
Earth’s atmosphere filters out most of the electromagnetic waves except for visible light and radio waves. UV, X-rays and gamma rays are filtered out, these are harmful to humans. 3. identify methods for the detection of various wavebands in the electromagnetic spectrum  Radio waves are detected with radio receivers that are connected to aerials.  Microwaves are detected with piezoelectric crystals.  Visible light is detected by photoelectric cells.

4. explain that the relationship between the intensity of electromagnetic radiation and distance from a source is an example of the inverse square law: I  d12
Electromagnetic radiation attenuates over distance, i.e. the further you are away from an electromagnetic source the less the intensity will be. This can be applied to light, as if you move away from a light it will be less bright. The Intensity is proportional to the inverse of the distance square, or I  d12

5. outline how the modulation of amplitude or frequency of visible light, microwaves and/or radio waves can be used to transmit information
Modulation of radio waves, both amplitude and frequency modulation are used today in AM/FM radio and television. The changes in the...