The number of cycles the current makes in one second is referred to as the frequency, and the frequency of the house current referred to above is 60 cycles per second. We call it a 60-cycle current.
Another form of current which enters largely into Radio is pulsating direct current which can be considered as a combination of A.C. and D.C. currents. Pulsating current flows always in the same direction but its strength is not steady--it increases and decreases periodically.
It is this type of D.C. current that we get from the rectifying tube in “B” eliminators before it is smoothed out with filters used in eliminators. Figure 6 shows how a pulsating current may be represented. Note that the curve is always above the zero line--meaning that the current moves only in one direction.
Fig. 6
The wave form of the curve shows that the current pulsates, its strength decreasing and increasing. It has all the appearance of a pure D.C. current as in figure 4 combined with a weak A.C. current. The A.C. portion is referred to as the “ripple.”
We shall meet pulsating direct current frequently throughout our Radio studies. Besides being in our D.C. power socket and our A, B, and C supplies, it is present in vacuum tubes, audio transformers, loud speakers. It is one of the chief jobs of a Radio receiver to separate and combine the A.C. and the D.C. parts of pulsating current and use only the one needed.
PRIMARY BATTERIES
Batteries, as we know them, are made up of a number of single chemical cells. Strictly speaking, a single cell is not a battery--two or more connected together form a battery of cells.
