Name(s) _________________________________________________________ Hr. ____
Capacitor activity with phet simulation
Resistors are important devices we can put in circuits. However, there are other things we like to add
to circuits, too.
In this activity,
we will learn all
about the
capacitor. A
capacitor is a
device in a circuit
that can act like a
battery. It can
provide electrical
energy to a
circuit just like a
battery.
However, it is a
bit different than
a battery. It can
be ‘charged’ up
and then
‘discharged’ many times. Many types of batteries CAN NOT be reused once depleted of its energy;
however, some batteries are rechargeable.
If you look at the picture above you will see different types of capacitors. Just like a battery,
capacitors have two leads or connectors.
If you discombobulate a ‘cap’ you will find a coil of
two foil sheets (at least with some types). The foil
sheets have a thin divider between them. Often this
divider is made of a waxy paper and acts as an
insulator. There also may a coating of an electrolyte
on the paper.
During the investigation, you will set up a capacitor circuit using the pHET online simulation. The
goal is to learn about how capacitors work. Are you ready to get rollin? Let’s get started.
Capacitor phet activity, p. 1
What is a capacitor?
Discharging or Neutralizing a
capacitor:
Capacitor phet activity, p. 2
Using PHET to construct a resistor-capacitor (RC)
circuit:
You will use a different PHET simulation this time: Circuit
Construction Kit (AC+DC), Virtual Lab:
http://phet.colorado.edu/en/simulation/circuit-construction-kit-ac-virtual-lab
Make sure to run the correct simulation.
Construct a SERIES circuit with one battery, wires, one light bulb, one resistor, one ammeter,
capacitor, switch, and voltmeter. Also click the ‘stopwatch. ’Here what it will look like:
Change the batteries voltage to 50 V (right click)
Make sure the resistor is at 5 Ohms (right click)
Make sure the light bulb is at 5 Ohms (right click)
Leave the switch open until ready
Make sure your capacitor is uncharged (right click)
Make sure your capacitor has a capacitance of 0.1 F (right click)
Put the voltmeter across the capacitor (it should say 0.00 V)
See the next page for further instructions.
Capacitor phet activity, p. 3
RESISTOR-CAPACITOR CIRCUIT 1
Now, we plan on switching the circuit on with the switch and turning on the stopwatch. However,
before we do this, let me tell you that when you activate the switch, there will be lots of changes. You
will get changes to your ammeter, changes to what the capacitor looks like, changes to your light bulb,
and changes to your voltmeter. You will have to watch carefully.
OK, so here is what I would like you to do:
Turn on the stopwatch and then quickly activate the circuit with the switch. Use the button at the
bottom of the simulation to start everything. Watch what the ammeter does, what the voltmeter
does, what happens visually to the capacitor, and what happens to the light bulb. Time this until the
voltmeter reads the same value that the battery has (50 V)
If you have all the circuit set up correctly, it might take you around 9 seconds or so.
1. What happened to the brightness of the light bulb as the capacitor charged up?
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2. How did the readings on the ammeter change as the capacitor charged up?
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3. How did the readings on the voltmeter change as the capacitor charged up?
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3. How did the readings on the voltmeter change as the capacitor charged up?
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4. What happened to the speed of the capacitor charging as the voltmeter was getting closer and closer
to 50 V?
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5. This is what your capacitor plates looks like as it charges up:
Capacitor phet activity, p. 4
Describe what is happening to the charge on the top plate as the capacitor charges up:
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Describe what is happening to the charge on the bottom plate as the capacitor charges up:
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RESISTOR-CAPACITOR CIRCUIT 2
Modify the circuit by doubling the resistance of the resistor and doubling the resistance of your
light bulb. Change both of these from 5 Ohm up to 10 Ohms each. Reset the stopwatch and the
circuit and make sure your capacitor is discharged. Keep everything else the same.
We have effectively doubled your resistance now (it was 10 Ohms total which included a 5 Ohm
resistor and a 5 Ohm light bulb. Now we have increased the resistor to
Now activate your circuit and time how long it takes for the voltmeter to get to 50 V.
It should take your circuit more time, for me, it took around 18 seconds.
Compare the charging time now relative to the first circuit?
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Why does it take longer to charge up your capacitor?
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RESISTOR-CAPACITOR CIRCUIT 3
Keep everything the same as in circuit #2, but double the capacitance of the capacitor. Change it from
0.1 F to 0.2 F. Reset the stopwatch and make sure your capacitor is discharged.
Now activate your circuit and time how long it takes for the voltmeter to get to 50 V.
It should take your circuit more time, for me, it took around 36 seconds.
How did this charging time relate to the charging time of your second circuit?
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Why does it take longer to charge up your capacitor now?
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Good job on capacitors!
Capacitor phet activity, p. 5