- Whilst an electric field is caused by a change in voltage (charge), a magnetic field is caused when electric current flows. The greater the current the stronger the magnetic field.
- An electromagnetic wave is the result of the interaction of an electric and magnetic field because an electric field induces a magnetic field and a magnetic field induces an electric field.
- An electromagnetic wave can be induced when either the charge of an electric field changes or when the current of a magnetic field changes or when they both change together.
- The waveform, wavelength and frequency of an electromagnetic wave result from the rapid periodic succession of transitions between the electrical and magnetic components and the forward propagation of the wave through space.
- When electric and magnetic fields come into contact to form electromagnetic waves they oscillate at right angles to one another.
- The direction of propagation of an electromagnetic wave is at a right angle to the electric and magnetic fields.
- The velocity at which electromagnetic waves propagate in a vacuum is the speed of light which is 300,000 metres per second.
- Once an electromagnetic wave propagates outward it cannot be deflected by an external electric or magnetic field.
- The reason an electromagnetic wave does not need a medium to propagate through is that the only thing that is waving/oscillating is the value of the electric and magnetic fields.
All electrically charged objects have an electric field around them.
There are two types of electrical charge:
With this in mind:
- If two objects with the same charge are brought towards each other the force produced will be repulsive and it will push them apart.
- If two objects with opposite charges are brought towards each other the force will be attractive and it will pull them towards each other.