Wayne Parham Messages: 18789 Registered: January 2001
Illuminati (33rd Degree)
You can find inductance by rearranging the inductive reactance formula, X = 2πFL. Measure the voltage across the resistor and find the current through the circuit using Ohm's law, I = E/R. Since it's a series circuit, that will tell you the current through the voice coil. Now measure the voltage across the voice coil at whatever frequency you are interested in. Don't just assume it is the difference between the source voltage and the resistor's voltage drop - it won't be. The coil and resistor are out of phase, so their voltage drops don't equal like in circuits with pure resistance. After finding the voltage across the voice coil and the current flowing through it, you can find its impedance using Ohm's law, Z = E/I. Substitute Z (impedance) for X (inductive reactance) and rearrange the formula to find inductance, L = 1/2πF.
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