1. Is a Spool of Hookup Wire an Inductor? We started with 100 feet of 22 gauge wire…

2. First, a Measurement Using an LCR meter we measure the wire’s inductance to be 731.8µH at 10kHz. The meter says it’s an inductor.

3. Let’s Test with a Circuit We decided to measure phase shift with a simple series RL circuit measured at 10kHz. A 45 o shift should occur when X L = R. Inductive reactance is computed by: X L = 2πfL X L = 6.28 x 10kHz x 731.8µH X L = 45.957Ω We used a 46.6 Ω resistor in our circuit to match the X L at 10kHz.

4. Connections to Signal Generator and Scope

5. Output Compared to Input The larger, yellow waveform is the source while the smaller is the signal across the resistor. There is phase shift! According to Ө = tan -1 X L /R Ө = tan -1 45.957Ω / 46.6 Ω Ө = 44.6 o

6. Measuring the Phase Shift This is a better look at the waveforms. Start by equating scope divisions to degrees. Our source waveform shows each horizontal division is equivalent to 36 o. In an inductive circuit, the voltage across the resistor lags the source voltage. This is clear in the image. 180 o /5 Div = 36 o per division

7. Measuring the Phase Shift (continued) Measuring the phase shift between the two waveforms involves interpreting the difference in spacing between similar points on each waveform. The source crosses zero going negative 1.3 divisions before the resistor output waveform does the same. Since each division is equal to 36 o the phase shift for the circuit is 1.3 x 36 o = 46.8 o - Close to 45 o Difference between source and output is 1.3 divisions

8. What Happens if We Unspool the Wire?

9. Here is the circuit with the hookup wire fully unspooled. Not much to look at because the wire is draped all over the lab and the resulting circuit is just the resistor connected to the signal generator with 100 feet of wire. We should expect the uncoiling of the wire to substantially affect the inductance properties and affect the phase shift.

10. What Happens if We Unspool the Wire? This is the source voltage compare to the resistor voltage with the spool uncoiled. The two signals are virtually in phase which is the outcome expected in a purely resistive circuit.

11. Coils of Wire Have Inductance!