Hi everyone. So we're going to learn how to charge and discharge a capacitor. Now what I have set up
on my circuit here is, I have one 100 micro farad capacitor, two ten kilo ohm resistors. I have a
jumper wire here, and I'll be using another jumper wire later on. Right now everything is set up in a
series circuit. I have two 10 kilo ohm resistors in series with my capacitor. Now this jumper
wire is also in series with the circuit. So what do I want to do?I have my battery pack
setup right here, and I want to charge up this capacitor using my batteries. Before I do that,
I want to go ahead and measure what the voltage is across my capacitor. So to do that,
I am going to place my probes into the breadboard, which you can do if you put a decent amount of
force on the probes. Okay now I'm going to turn on my meter. I'm measuring zero volts,
which is what I expect to get. That's important to know that capacitors do have a polarity. You'll
see a small leg and a large leg. The small leg being the negative polarity, the large leg being
the positive polarity. Okay I'm going to go ahead and turn the display light on. So we can see how
the voltage changes, if at all. I'm expecting as I make my connections that the voltage will rise.
Okay, so my voltage rises up to the same voltage. So the voltage across my capacitor rises to the
same voltage as the voltage of my power supply. In this case, four AA batteries. All right,
now let's go ahead and remove these. Okay so I've removed the power supply altogether,
but you notice I'm still reading a positive voltage. That's because the
capacitor is charged up, and the voltage across that capacitor is the same. You see
it's slowly going down due to leakage current. Now if I make a connection in
the circuit from this side of the circuit, to the other side, and notice it starts to drop.
Now the speed at which it drops is dependent on my time constant. So, for instance, that time
constant is dependent on both the size of the capacitor, and the resistance in the circuit.
So you saw how quickly it discharged there. I'm going to charge it up one more time. Once again,
I'm charging up my capacitor. Okay, that's good enough. Now what I'm going to do is, I am going
to bypass one of the resistors. So I'm going to very carefully touch this part of the resistor,
and this side of my capacitor. Okay, and it discharged much quicker at that time.
Let's do it one more time...
charging up.
Okay, this time I'm going bypass the resistors all together. Okay, and you can see it discharged very
quickly that time, which is one reason if you have a very large capacitor with a very high voltage,
you need to be very careful, because those capacitors can discharge extremely quickly,
and that can be dangerous in certain circumstances. Okay so in the comment
section I want you to tell me what's going to happen if I added an additional 10 kilo
ohm resistor into the circuit. Tell me what's going to happen to the time constant,
the time it takes to charge the capacitor and the time it takes to discharge the capacitor.