The Production of Electromagnetic Waves By a Wire Aerial
If an alternating current is passed along a piece of wire, a constantly changing electric field will be produced because the distribution of electric charge is changing – remember that an electric field is produced by a distribution of charge. In addition, a magnetic field will be produced by the current, and since the current is changing constantly, so will the magnetic field be.
The direction of inth electric field is oriented in the same direction as the current, and the magnetic field will be perpendicular to this. The magnetic and electric fields move away from the wire as a coupled system. A changing magnetic field induces a changing electric field and vice versa.
In order to be received as a single, the wave must induce an electric field in a receiving aerial consisting of a wire. The receiving aerial must be oriented vertically just as for the transmitting wire. The waves produced by the transmitting wire are vertically polarized, and just as for a polarizing filter, the receiving aerial can be rotated, with the received signal changing from maximum to zero to maximum as the receving aerial is rotated from vertical to horizontal to vertical.