Physics 109 - RL Time Constants

In this experiment you will study another physical system that exhibits an exponential decrease as a function of time. The combination of a resistor R and inductor L in series exhibits an exponential transient response which you can observe by measuring the volage across the resistor in the circuit below.



Instead of observing a decay in a single shot by opening a switch, you will repeatedly trigger the transient by using the AC function generator to generate SQUARE WAVES. Every time the voltage of the generator jumps up or down, you will see the transient response to the sudden change.

 Theoretically, the time constant, tau, in this circuit is given by the ratio L/R. The goal of the experiment is to check this theory and determine the value of the inductance L. You should initially use a range of resistance values between 10 and 2000 Ohms and take at least 10 measurements. Plot 1/tau versus R for your initial check of the relationship.

Marking Scheme

11 marks: includes high quality measurement of time constant versus resistance, plotting and fitting a model to the data, and conclusions