5/26(RL circuits/ Oscilloscope)

Lab Day: 5/26 RL circuits (Oscilloscopes, Inductors)

Purpose: We look at RL circuits and use oscilloscopes to analyze the relationship. 

We began class by looking at inductors and applying Faraday's law where a changing current will cause an induced emf in the inductor.  The graph below shows that as time goes on, the current will increase exponentially.  Initially when the switch in the circuit is closed, no current is flowing and the voltage across the inductor is the same as the voltage source. Then as the current increases it starts plateauing and reaches a steady state consistent with our equation.

Next, we used the equation for inductance using a given resistance and found that the inductor had an inductance of 760 mH. we found the resistance of the copper wire in the given inductor based on calculations below after find the inductance of the given inductor. The resistance calculated is quite small.

Introduction to the Oscilloscope: Measuring Inductance

In this experiment, we used the oscilloscope shown in the picture connected to a function generator. The display shows a square wave form initially shown in the picture. We adjusted the knobs and played around with the controls to get the voltage to be displayed in this shape.

We then attached an inductor in parallel to the oscilloscope and adjusted the positions again and it showed an altered wave form from our original display.

The results showed expected behavior as the induced emf was shown across the inductor. We then calculated the inductance using the wave form measured from our oscilloscope and found experimentally that the inductance across the inductor is 703 mHenrys. The percent error is 7.5% from our theoretical calculations of our inductor used which is pretty good. 

LR Circuit Problem

We went further to look at an LR circuit where we have an inductor and two resistors connected in our circuit. Using the equation I=Imax(1-e^-t/tao) we found the current flowing through. Below shows calculations using kirchoff's rule and ohms law to solve for time constant, energy, and current.

Conclusion: The voltage and current is seen to behave differently when an inductor is added to the circuit and the current is seen to increase rapidly and reaches a steady state as seen in the experiments of our oscilloscope and RL Circuit problems.