Certified Radio-Trician's Course(REG. U. S. PAT. OFF.)
NATIONAL RADIO INSTITUTE
WASHINGTON, D. C.
SIMPLE CIRCUITS
In previous lessons, when we studied the production and some of the actions of electricity, we met the word “circuit” several times. Whenever we speak about electricity in action, that is current, we must speak about circuits--for current will act only when in a circuit.
Radio-Tricians speak in terms of circuits--you might hear on mention a tuned radio frequency circuit, or a superheterodyne circuit, or the circuit diagram of some particular receiver. Very obviously, it is important that we get a clear idea of what we mean by Radio Circuit.
The word itself is very clearly connected with the word “circle.” In fact both of them are taken from the same Latin word, which peculiarly enough is the same as our English word “circus.” The Roman “circus” was the track on which chariot races were held. Our modern circus takes its name from the fact that in the main tent there is always a track on which some of the performance is held, usually races of some sort or other.
A circle is an unbroken ring--and a circuit is an unbroken path over which electrons can flow. The main point of comparison between a circuit and a circle is that both must be unbroken, that is, complete, before they are rightly called a circuit or a circle. However , an electrical or Radio circuit need not be circular in form, the chief requirement being that a circuit provides a complete path for moving electrons, that is, current flow.
Having spoken about current flowing in a circuit, we can see that one essential part of any circuit is a source of e.m.f. But the whole purpose of a circuit is to get the e.m.f. supplied by the source to do some useful work--therefore another essential part of a circuit is the “load,” the device in which electrical energy is converted into some other kind of energy, and made use of. To connect the load and source of e.m.f., there are conducting wires which complete the circuit.
Thus in the circuit shown in Fig. 1, the dry cell is the source of e.m.f., and light bulb is the load. And this is a good
