Day 19 Charge Buildup and Decay in Capacitors

At the beginning of the class, we did an experiment called charge buildup and decay in capacitors.

We made a circuit of battery, a capacitor, and a switch in series. The bulb gets dimmer and dimmer as the switch is closed more. Then we take away the battery out of the circuit and the bulb lit again and got dimmer after times.

This graph shows the brightness of the bulb as the time went up when it is placed across a charged capacitor without the battery. We can see that the bulb is less bright overtime.

In these two pictures, we did an activity where we hooked up two capacitors to 2 batteries with different voltages and measure the capacitors' final voltages. And we found that Vtot= 1/2(V1+V2).

In this picture, we did an experiment called quantitative measurement on an RC system. We built a RC system with a battery, a capacitor, a resistor, a voltage measuring lead, a computer, and 6 wires.

This is the voltage vs. time graph we made by logger pro about two processes, charge the capacitor (red) and discharge the capacitor (blue)

We used the equation V=IR and Q=CV to find the unit of RC, so the unit is second.

We used the equation V=Q/C, V=IR and I=dq/dt = -q/RC to find that q = e^(-t/RC)

This is an experiment where the two wires together will explode if turn on the green box.

In this picture, we graphed I vs. t graph by analyzing the V vs. t and brightness vs. t graphs.

We did a practice problem on RC circuit. There are two equation, one is for charge, the other is for dischage.

Then, we found the RC is 1s and another loop's RC is 0. Then we used the equation of charge to find that t is 1.1 second.

In this picture, the switch is turned off, and we used the equation of discharge to find the time is 149s.

Conclusion

In today's class, we did a few experiments and activities on ideas of charged capacitor, discharged capacitors, and RC circuit in order to understand how they work. We also learned to find RC and time constant in a RC circuit.