stance reduces the potential gradient by a factor of four. Magnetic fields Magnetic fields are also important. Like electric charges, magnets attract and repel one another. Analogous to the positive and negative charges, magnets have two types of pole, namely a north and a south pole. Like poles repel and dissimilar ones attract. In the case of magnets it is also found that the magnetic field strength falls away. It is found that it falls away as the inverse square of the distance. While the first magnets to be used were permanent magnets, much later it was found that an electric current flowing in a conductor Direction of current flow Lines of magnetic force Figure 2.3 Lines of magnetic force around a current carrying conductor 20 Newnes Guide to Radio and Communications Technology generated a magnetic field. This could be detected by the fact that a compass needle placed close to the conductor would deflect. The lines of force are in a particular direction around the wire as shown. An easy method of determining which way they go around the conductor is to use the corkscrew rule. Imagine a right-handed corkscrew being driven into a cork on the direction of the current flow. The lines of force will be in the direction of rotation of the corkscrew. Radio waves As already mentioned radio signals are a form of electromagnetic wave. They consist of the same basic type of radiation as light, ultraviolet and infrared rays, differing from them in their wavelength and frequency. These waves are quite complicated in their make-up, having both electric and magnetic components that are inseparable. The planes of these fields are at right angles to one another and to the direction of motion of the wave. These waves can be visualized as shown in Figure 2.4. The electric field results from the voltage changes occurring in the antenna which is radiating the signal, and the magnetic field changes result from the current flow. It is also found that the lines of force in the electric field run along the same axis as the antenna, b