AC1 Fundamentals Unit 7 – Capacitive Reactance
Exercise 3 – Parallel RC Circuits
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to determine characteristics of parallel
RC circuits by using calculated and measured values. You will verify your results with an
oscilloscope.
EXERCISE DISCUSSION
- In a parallel RC circuit, total capacitive reactance is found by taking the inverse of the sum of
the reciprocals. - If only two capacitors are in parallel, the product-over-sum method can be used.
- Capacitive reactance decreases as the number of capacitors in parallel increases; this results
in higher circuit current and lower circuit impedance. - The equivalent circuit has two distinct branches: one resistive and one reactive.
- Voltage drop across parallel branches are equal. Ohm’s law is used to find the branch
currents. - Total circuit current is the square root of the sum of the squares of the branch currents.
- Circuit impedance is found by using this formula: Z = (R x XC)/[sqrt(R^2 + X^2 C)]
- The phase angle between the applied voltage and circuit current increases as capacitance is
increased.