WavesWaves can be described as a transfer of energy. They can occur in one, two or three dimensions, depending on the nature of the wave and the medium. Waves can be classified as mechanical or electromagnetic. Mechanical waves require a medium and can be transverse or longitudinal. Electromagnetic waves do not require a medium and are all transverse. Figure 1.a. shows the image of a transverse wave, figure 1.b. shows the image of an electromagnetic wave. In special circumstances standing waves can be produced, this occurs when a sound wave interferes with its own reflection. Sound waves overlap to produce a stable energy distribution, standing waves do not move, but a pattern forms with regions of zero oscillation (called nodes) and maximum oscillation (called antinodes), both fixed in space. Figure 1. c. shows that these two waves have the same amplitude and frequency moving in opposite directions, when they combine you can see a fixed pattern of nodes and anty-nodes. The electromagnetic spectrum is the range of electromagnetic waves, they vary in frequency and wavelength. Radio waves have the longest wavelength and lowest frequency, while gamma rays have the shortest wavelength and highest frequency. Figure 1.d. shows an image of the electromagnetic spectrum. All electromagnetic waves are transverse and can all travel through a vacuum. They also require no support. The sun produces all electromagnetic waves, they are produced by a vibrating electric charge, which means they are made up of both an electric and magnetic component. All electromagnetic waves propagate at the speed of light and in a straight line, unless there is a change in the medium. If there is a change, then the ...... middle of paper ......h day. Each satellite transmits radio waves to Earth containing information about its location and time. Anyone can obtain this information thanks to GPS receivers, which identify and decipher information from satellites. Positioning information from GPS satellites is sent as repeating codes that a GPS receiver can use to determine its position on Earth (latitude and longitude). ) with an accuracy of approximately 10 m. There are more sophisticated receivers that can determine the position with an accuracy of a few millimeters. The codes that form the structure of the GPS signal are superimposed on two carrier waves. The carrier frequencies and signal frequencies are a direct result of the onboard atomic clock oscillator frequency of 10.23 MHz. figure 1.g. shows the image of the earth surrounded by GPS satellites.