Electrical Engineering is a free introductory textbook to the basics of electrical engineering. See the editorial for more information....

Series Circuits With Resistance and Capacitance

Author: E.E. Kimberly

In the circuit of Fig. 5-15 the same current flows in both the resistance and the reactance. The resistance voltage drop is in phase with the current, and the capacitive reactance voltage drop lags the current by 90°, as indicated in Fig. 5-16. The angle 0 is the characteristic angle.

Fig. 5-15. Resistance and Capacitive Reactance in Series Fig. 5-16. Voltage Diagram for Circuit of Fig. 5-15

Example 5-7. - A resistor with R = 30 ohms is connected in series with a .condenser with C = 50 microfarads to a 220-volt line whose frequency is 60 cycles. How much current will flow?

Solution. - The capacitive reactance is



The current is found as follows:


Example 5-8. - A resistor whose resistance is 10 ohms has a maximum safe current capacity of 5 amperes. It is to be used on a 220-volt, 60-cycle line in series with a condenser. What must be the capacitance of the condenser to limit the current to a safe value?

Solution. - The impedance is




from which C = 0.000061 farad or 61 microfarads

Last Update: 2010-10-06