Capacitor Charge and Discharge (17th Day)

Spring 2015
Professor Mason
April 30 Class

Capacitor Circuit Sketch

In class, we needed to make a sketch of circuit containing light bulbs, capacitor, switch, and batteries in order to answer the questions from lab manual. We first need to answer part a, which includes light bulb #14 (round), capacitor, battery, and a closed switch, however nothing happened to the light bulb. Then, part b required us to take off the battery and connect the wires to the switch, capacitor, and light bulb directly. The result was that the light bulb lighted only for a little while, then it became dimmer and finally died. This happened because the energy stored in capacitor from the battery has been used up for the bulb to light. After that, we needed to do part C, which required us to do a graph of brightness versus time; the result is shown in the picture attached above. 

Based on what the professor said, a part of equation for this case is time constant (T), which has a definition of time for a constant to charge the capacitor; T is perpendicular to RC (resistance in capacitor). Then, we needed to connect two capacitors into super capacitors (series); when it was first connected, the bulb did not light because the batteries are charging the capacitor; then, after we took off the batteries, the bulb would light because the capacitor already had stored energy in it. After that, we put on the batteries again, and the bulb lighted only for a little while, then it got dimmer after a while.
In class, we also needed to find an initial voltage for each capacitor. We needed to measure three batteries with multi-meter, attach two set of circuits together along with two capacitors. Then we needed to find the voltage in the capacitor after being discharged with multi-meter.

Logger Pro Graph

 In class, we also needed to do an experiment with logger pro. We needed to attach the multi-meter to capacitor, then measure it while charging or discharging. Then, we needed to make a graph in logger pro using voltage probe as well. The red lined graph shown in the picture above shows the movement of the capacitor when we hit the collect button while discharging the capacitor, followed with hooking the alligator clip together in order to discharge it.

The blue lined graph shown in the picture above shows the movement of the capacitor when we hit the collect button after hooking them together(discharge), then attach them back together to batteries.
After all of that, we also needed to make a curve fit out of the graphs, and the closest we could find was the natural exponential fit. The simplified formula for the fit by hand is shown in the picture below, as well as the calculations.

In class, we found out that brightness is perpendicular to P, [P = IV]. We also found out that as P decreases, V increases, and I has to decrease. All the formulas and equations are shown in the picture above. As well as the equations, the graph is also shown in the picture attached below (V vs t), (I vs t), and (Brightness vs t).

Experiment: Exploding Capacitor

In class, professor Mason did an experiment which involved a capacitor. He did something with the capacitor in order to make the capacitor boiling hot. After a while, the capacitor exploded into pieces. In the photo shown below, it is the can of capacitor that we found. 

Calculations

 In class, we did some calculations including circuit loop and graphs. On the circuit shown in the picture above, it has a switch that determines where the loop is going. When the switch is opened, only the top circuit works. However, when the switch is closed, the loop is going around all the circuit. In this case, we use an equation of [Q = Qo e^-t/RC] or [T = RC]. After we did all the calculations, we found out hat the time it took for a capacitor to charge in a full loop is 2.5 minutes.