example of a fundamental electrical circuit. It is shown schematically in Fig. 2.
The switch shown in Figs. 1 and 2 is provided so that there will be a means of opening and closing the circuit without the necessity of disconnecting either the dry cell or the lamp. You remember that a single break in a circuit will prevent current from flowing in it--a switch as shown, placed anywhere in the circuit provides an effective control--when opened, the current will not flow and the lamp will not light--when closed, the circuit is complete, current will flow and the lamp will light.
It is important to remember that the switch can be in any part of the circuit--it could be anywhere in the left conducting wire, as well as any place in the right conducting wire.
The source of supply may be one or more dry cells, a storage battery, a generator, in fact, any kind of generating device, or the source of supply may be a wall or panel socket, as in the supply for an individual light, for example, in the house line. The load in the circuit may be an electric bell, a light bulb, an electric motor, a coffee percolator, a vacuum tube or a complete Radio set. In the simple circuit shown in Fig. 1, the load is, of course, the lamp which is a means of converting electrical energy supplied by the dry cell into light energy. The light is incidental to the conversion into heat energy as you probably know, but it is the light we are interested in because that is what we make use o. This simple circuit is interesting to us as Radio-Tricians because it is very similar to the filament circuit in a Radio receiver, but in this case we are interested in heat, rather than light, for filament heat is necessary for the operation of vacuum tubes.
You will want to know now, how electrical energy is converted into heat energy in an electric light bulb or in a vacuum tube. Referring again to Fig. 1, “R,” in the center of the lamp, is a very fine carbon or Tungsten wire, having high resistance. In a previous lesson it was mentioned that the effect of resistance in an electrical circuit was to slow down current flow, because electrons can’t pass through a resistance readily, and the electrons becoming violently agitated, bump against each other with terrific speed, causing the resistance to become hot. When metal is white hot it glows brightly. Put this hot metal into a vacuum, as it is in a light bulb, and the result is an intense bright light.
