Lesson One : Electromagnetic Wave
Electromagnetic waves are generated when an electric charge begins to accelerate (that is, when its velocity begins to change). The wave then propagates by two mechanisms that were discovered by Maxwell.Electric charges generate electric fields. This electric field is responsible for a variety of effects observed in everyday life. For example, electric fields are responsible for moving power through power lines and are generated by running a comb through your hair. When an electric field begins to change it, in turn, creates a changing magnetic field.
Magnetic fields are generated by magnets. The attractive forces generated by magnets are responsible for keeping your pictures on the front of your refrigerator. When magnetic fields change, they create changing electric fields.
Thus, when an electric charge accelerates, its electric field changes. This change creates a corresponding changing magnetic field. This field then creates another changing electric field and the process continues perpetually as the wave travels through space. As a result, electromagnetic waves are said to be self-propagating.
Electromagnetic waves traveling in empty space have a speed of 186,000 miles/second, a speed known as the speed of light (usually represented by the letter c).