Fig. 1,326,—Circuit diagram illustrating the distinction between capacity in series and capacity in parallel. The condition for capacity in series is that the circuit must be discontinuous as at M; for capacity in parallel the main circuit must be continuous; this means that the capacity must be inserted in a branch of the main circuit as at A. In the figure the capacity S is connected in series with respect to the branch, that is, the branch is discontinuous, but it is in parallel with respect to the main circuit, when the latter is continuous, that is, when the switch W is closed. If W be opened, the main circuit becomes discontinuous and S is changed from in parallel to in series connection.
Ques. In circuits containing resistance and capacity upon what does the amount of lead depend?
Ans. Upon the relative values of the resistance and the capacity reactance.
Ques. Describe the action of a condenser when current is applied.
Ans. When the current begins to flow into a condenser, that is, when the flow is maximum, the back pressure set up by the condenser (called the condenser pressure) is zero, and when the flow finally becomes zero, the condenser pressure is a maximum.
Fig. 1,327.—Current and pressure curves showing that the condenser pressure is 90° ahead of the current. A current flowing into a condenser encounters a gradually increasing pressure which opposes it, beginning from zero pressure when the current enters at maximum flow and increasing to the same value as the current pressure, at which time the current ceases to flow. Hence, since the current varies from zero to maximum in one quarter period, or 90°, the phase difference between current and condenser pressure is 90°. The condenser pressure reaching a positive maximum when the current starts from zero on the positive wave, is 90° ahead of the current.
Ques. What does this indicate?
Ans. It shows that the phase difference between the wave representing the condenser pressure and the current is 90°, as illustrated in fig. 1,327.