t was a LR circuit. The back emf (xL) is equal to the rate of change of the current times the inductance of the coil (L). The inductance has units of henry (H), which is equal to the units Vs/A. Here is the equation:xL = -L (DI / Dt)In this case, tau has the following equation:t L / RResultsIn this lab, we learned about RC and LR circuits. In part one of the lab, the percent error between our experimental tau versus the theoretical tau was very good. The average was 4.0 % and it ranged from 0 % to 12.0 %. In part two of the lab, we didn’t do so well. I think the graph for this part was wrong or that we got very bad data because the percent error was 124% and we know that it physically can’t be more than 100 %. In part three, we got two percent errors. The first one was 3.5 % and described the relationship between the actual value of tau, which was 33.33 microseconds versus the experimental tau, which was 34.5 microseconds. The second percent error described the relationship between the experimental tau, which was 34.5 microseconds, and another experimental tau, which was 26 microseconds. This percent error was 24.64 %. If you compared the second experimental tau to the actual value, you get a 22.0 % error. Some of the error sources were: the estimation of the divisions on the oscilloscope screen and especially human error. ...
