TinkerCad: Circuits With Capacitors
A capacitor is a component that stores electrostatic energy. This is a form of potential energy. Capacitors contain two electrical conductors and are separated by an insulator. The conductors are thin films of metal. The insulators can be glass, ceramic, plastic, or air. When a capacitor is connected to a battery, positive charges collect on one plate and negative charges collect on the other plate. When the capacitor is filled with an electric charge, it will not allow current to flow through the capacitor. The electric charge can be released by the capacitor into a circuit. Capacitors store electrical energy as potential energy and release it into a circuit as voltage and current.
Teachable Moment: Take a look at the various materials used as insulators and think about which material might provide the best resistance. What makes a good resistor? Most capacitors use air for the capacitor because air is a much better resistor. Why is air a much better resistor? Think about the properties of air and the other resistor materials.
In this circuit, we will create a circuit that uses a capacitor to store the energy from a battery and then discharge that energy into an LED. To accomplish this, we will need two buttons to control the flow of voltage to the capacitor and to the LED. One button will allow us to send electricity to the capacitor while the other will prevent the electricity from going to the component until we are ready.
Create a new circuit project.
Place a small breadboard onto the work area. Place a 9 volt battery on the right side of the breadboard and place a push button switch to connect the top half of the breadboard with the lower half.
Click the All Components section to search for the capacitor. The capacitor we will use in this circuit is not part of the basic components.
Look for the Polarized Capacitor.
Place the Polarized capacitor in the top half of the breadboard. Leave three columns to connect jumper wires. This capacitor is polarized, so that means that it has a positive and a negative terminal. The negative terminal is the one that has a strip above the terminal wire. Align the positive side of the capacitor to the left side of the switch.
Connect the negative part of the battery to the top of the breadboard and the positive part of the battery to the bottom of the breadboard rails.
Connect a jumper wire from the positive rail to the push button. Remember, the opposite end of the switch is used to connect circuits.
We need to connect the negative connector of the capacitor to the negative rail, but it is too large to see the connector row.
Move the capacitor to the left or right and connect a jumper wire to the row where the negative connector for the capacitor would be.
Move the capacitor back into place. Make sure to leave two columns between the switch and the capacitor for jumper wires.
The capacitor is not connected into a circuit. Pressing the button will send current to the capacitor. The capacitor will collect this current until it is full. It is possible to overfill a capacitor and that would damage the capacitor and could be dangerous. Capacitors store lots of energy like a battery.
To discharge the capacitor, we need a component. We will use the trusty LED to help us see the capacitor’s discharge. Place an LED in the lower half of the breadboard. You might need to go back to the Basic Components section to get the LED.
Connect jumper wires to other rows on the left side of the capacitor. We will use these rows to connect to the LED on the lower half of the breadboard with more jumper wires. Align the wires to the Anode and Cathode rows on the LED.
Go to the components panel and find another push button switch. Place the switch so that the left side of the switch aligns with the LED anode.
Shorten the positive jumper wire so it connects with the first push button connector.
Use a jumper wire to connect the negative voltage from the capacitor to the cathode of the LED.
The circuit is complete. Start the simulation then click the button on the right. This part of the circuit sends electricity to the capacitor. The other button is not pressed so that part of the circuit is open and does not allow electricity to flow.
Charging and Discharging the Capacitor
Hold the button down for a few seconds. Two to three seconds would be good. This simulates voltage being passed to the capacitor. We don’t actually see the capacitor charging. Capacitors charge rapidly so in a real-world capacitor the capacitor would be charged as soon as the button was pressed. The capacitor is now charged and will hold the electrostatic charge. Release the button to open the circuit to the capacitor.
Press the other button, and you will see the LED light for a few seconds and then dim away. The LED dims away because the electrostatic discharge from the capacitor drains away. If we could maintain the button pressed on the right side, then the LED would remain lit. The capacitor will receive a continuous charge which it would then release to the LED. Capacitors are used to store large amounts of electricity to feed the needs of large components.
Capacitors are used with devices like amplifiers so that they can supply large voltage when required. They are used for starting equipment that requires large amounts of current.
Stop the simulation and click on the capacitor. Look at the capacitor information panel. The capacitor is rated to store 16 volts. Different capacitors are constructed to handle different voltages.
Capacitors have a capacitance. Without getting very technical, this is the amount of charge the capacitor can hold. The amount of capacitance is measured in Farads in honor of Michael Faraday. We won’t go into the complexities related to calculating the capacitance of a capacitor. This information is provided on capacitors or on an information sheet when capacitors are purchased.
To demonstrate capacitance, change the capacitance to 2 in the capacitor configuration panel. The “u” in front of the letter “F” represents micro. A micro represents one millionth. This capacitor has a capacitance of 2 microfarads or 2 millionths of a farad. This is a very tiny amount but more than enough for our circuit.
Start the simulation and charge the capacitor. Press the button to release the charge into the LED. Not that the LED remains lit longer. The LED will remain lit for about five seconds.
The image below is an example of an information sheet that comes when capacitors are ordered. The capacitor outlined in red has a capacitance of 46 micro-farads with a tolerance of 10 volts.
Student Activity:
- Ask students to explain what is going on when the LED takes longer to turn OFF.
- Have the students create a table with the headings Capacitance and Time. List the capacitance from 1 to 10 down the column. Have students change the capacitance to each value and record the time it took for the LED to turn off.
- Have the students look at the data collected and ask them to determine if the time increase is consistent.
- Is there a relationship between the capacitance and the time it takes for the capacitor to discharge and the LED to turn off?
- Ask students to compare and contrast a capacitor and a battery.
- When would a capacitor be more useful than a battery?
- Ask the students to change the voltage rating from 16 to 3 and charge the capacitor. What happened? Why did it happen? Why didn’t this happen when the voltage rating was at 16?