What would happen to the filaments ? They wouldn’t light at all. The current would be side-tracked and kept away from the filaments, and the circuit would be “shorted.” This then, would be a short circuit, about which you have probably heard many times.. And short circuits are a frequent cause of trouble in Radio circuits--many times in your work as a Radio-Trician it will be necessary for you to track down short circuits and remove their cause so that current can flow over the proper path.
In any kind of electrical or Radio circuit, great care must be exercised to prevent the possibility of shorting. Conducting wires are insulated, oftentimes electrical and Radio apparatus must be mounted on non-conducting material, many types of insulators are in use to keep the current in the proper path so there will be no “short” either within the circuit or between one circuit and an adjacent circuit.
Fig. 9
The word insulate also is taken from the language of the old Romans. Their word “insula” meant island, a body of land surrounded entirely by water. A wire is insulated when it is surrounded entirely by non-conducting material. A piece of Radio apparatus is insulated when it is entirely surrounded by non-conducting material.
CONDUCTORS AND INSULATORS
All substances, natural or manufactured, can be divided for electrical purposes into three classes--conductors, resistors and insulators. Conductors are so-called because current can flow in them easily. Current will flow in resistors but not quite so easily, it will be held back. For practical purposes we say that current cannot flow at all through insulating material although this is true only up to a certain point, for a too high voltage will cause an insulator to break down and become a conductor.
