Cuthbert Nyack

The RL circuit is shown schematically above.
The Impedance of the circuit is Z = (R + jwL)
The magnitude of the impedance of the circuit is given by:-
|Z| = Ö(R2 + w2L2)
The phase of the impedance of the circuit is given by:-
Ðq = atan (wL/R)
The phase of the current and Vr is Ð-q.
Vl is advanced relative to Vr by 90°. q

The variation of the sinusoidal voltages Vs (green curve), Vr (orange curve) and Vl (red curve) are shown by the above applet as a function of frequency and time constant (T = L/R). Frequency is expressed in terms of 1/T. Two periods are shown for all frequencies. A Bode plot is shown in the background. The white line indicates the point on the bode plot at which the voltages are shown.

A phasor diagram showing the variation of Vr and Vl with frequency is shown above. The orange line represents the voltage across the resistor, the red line represents the voltage across the inductor, the green line represents the source voltage and the 2 purple lines complete the parallelogram showing that the resultant of Vr and Vl is Vs. Vl is always leading Vr by 90°. Note that at low frequencies most of the voltage appears accross the resistor while at higher frequencies the voltage is mostly accross the inductor.
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COPYRIGHT © 1996 Cuthbert A. Nyack.