AC1 Fundamentals Unit 4 – Inductive Reactance
Exercise 2 – Series RL Circuits
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to determine characteristics of series
RL circuits by using calculated and measured values. You will verify your results with an
oscilloscope.
DISCUSSION
- Total resistance of a series circuit is the sum of the individual resistors. Resistance increases
as the number of resistors increase, causing lower circuit current. - Inductors connected in series behave in a similar manner. Total inductive reactance is the
sum of the individual reactance. Inductive reactance increases as the number of series
inductors increase, resulting in lower circuit current and higher circuit impedance. - Impedance (Z) is measured in ohms and is the total opposition to current flow; it includes
both inductive reactance and resistance. - Resistance and inductive reactance cannot be added directly to obtain impedance.
- In an RL series circuit total impedance is found using this equation:
Z = sqrt(R^2 T + X^2 LT)
- A practical method of finding Z is to measure the total circuit current (IT) and divide it into
the applied voltage (Vac). Z = Vac/IT - In RL circuits, applied voltage is the square root of the sum of the squares of the voltage
drops. VGEN = sqrt(V^2 RT + V^2 XLT) - Since impedance is a phasor, there is a phase angle associated with it. The phase angle is
found with this equation: θ = arctan (XLT/RT)