Lab 17: Charge and Decay in Capacitors

First thing we did today was to charge and discharge capacitors, then we worked on the charge build up and decay in capacitors lab. To discharge a capacitor, we just connect the capacitor with the bulb holder, and to charge it, it must be connect to a voltage supply. When charging a capacitor, the brightness of the bulb decreases over time. We learnt that if the capacitance decreases, then the times it takes to charge also will decrease, and vice versa. Also, this charging time is also known as tau, which is the time it takes a capacitor to charge up to 37%.

Our graph of brightness vs time, indicates that the brightness of the bulb has an inverse relation with the capacitor because over time it gets dimmer.

Then our group used 3 batteries in series with 1 capacitor while the other group used 2 batteries in series with 1 capacitor, both groups were supposed to calculate the respective voltage. After knowing each voltage, we used three batteries in series connected with two capacitors in series in order to predict the final voltage. The final voltage resulted to be just the mean value of the two previous voltages.

 We started working on the quantitative measurements on an RC system lab. We grabbed 5 capacitors of 1000uF for this experiment. First we fully charged the capacitors with 3 batteries, then we graph the potential vs time using logger pro when we closed the circuit (discharging graph). We also graph the potential vs time when the capacitors were charging. Both graphs resulted to be exponential functions. The equation for discharging capacitor is V(t)=Voe^(-t/τ) and for charging capacitor is
V(t)=Vo(1- e(^-t/τ)).

Using the formula given by logger pro, we verified that the units where correct. Then using the formula τ = RC, we found the units for tau, which was supposed to be seconds.

Professor Mason showed us that if a capacitor is overcharged in the wrong direction, it will explode. Here is the capacitor after the explosion.

This is the time it takes the capacitor to charge.

This is the time it takes the capacitor to discharge.