R-L Circuits

Purpose:  We start to look into circuits that only involve resistors and inductors and do some calculations.

Working With Inductors

We revisit how to interpret the resistance of a typical resistor with color coded brands. We were given an inductor in which we measure its physical values to determine its inductance. We also learned how to write in engineering notation. We also calculated the resistance of the wire and found the the resistance is negligible when calculating the time constant. From this time constant, we are able to find the period, as the time constant was about one fifth the period. From the period, we were able to get the frequency needed for the experiment that proceeds.

Using The Oscilloscope On The Inductor

We create a circuit using a resistor and an inductor and a function generator. Once we determine the frequency needed for this circuit, we set the frequency and connect the circuit together. We, then, connect the oscilloscope to the inductor so that we can see the voltage across the inductor. The graph behaves in a way that we expected it to, as it shows us the behavior of the induced emf inside the inductor. From the graph on the oscilloscope, we were able to get some experimental values to calculate the experimental time constant with uncertainty and with the time constant, we were able to get the number of turns the inductor has.

An R-L Circuit

We were given a circuit to examine with 2 resistors and an inductor. The circuit is as drawn on the white board. We had to find the currents in the circuit at a specific time. We know that the current changes when there is an inductor because of the induced emf but we see that one resistor has no inductor along that wire and therefore, we are able to quickly get the current along that wire. The current stays the same along that wire the entire time but when we look at the current where the inductor is located, we have to calculate current with respect to time. To do this, we need the max values for current. We use the max values to plug into our formula for current with respect to time when an inductor is present and this allows us to calculate the current along the wire with the inductor. The last thing for us to do was to calculate the time for our inductor to reach 11 volts. For that, we had to look at how many volts the resistor along the same wire would have if the inductor had 11 volts and calculates the current along that wire using ohm's law. Once we have the current, we can then refer back to our equation for current along the inductor and solve for time.

Conclusion:  We took a look at how the voltage and current behaves when we have an inductor and a resistor in a circuit. We found that if a power supply operates at some frequency, the voltage vs. time graph shows us that the induced emf starts at a large value and steadily decreases with time. Then, the induced emf switches "direction" because of the frequency being outputted. We use what we learned about R-L circuits to solve a problem.