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Antennas
Antennas are one of the key pieces to a radio. Antennas come in a variety of shapes and sizes; they vary from large arrays to a small wire. Much of this variance is based on the broad use of radio waves and practicality; for instance you wouldn't use an antenna from a small radio to send a signal to a satellite.
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Antennas work by creating a resonating flow of charge along its element. The resonance is caused by a magnetic field fluctuating through an inductor that is fixed to a capacitor. As a magnetic field fluctuates across a conductor it causes charges to move. This motion causes an electro magnetic wave.
The relations between the electricity and magnetism are explained by Maxwell's equations. Maxwell's equations are four equations that relate magnetic fields electric fields and charges and current.