Learning goals
Mechanical energy can be transformed into electrical energy with a generator.
Electrical energy can be transformed back into mechanical energy with a motor.
Electrical energy can be stored in a capacitor. A capacitor stores electric charges, which flow and transfer energy when it is connected in a circuit.
A battery stores chemical energy that makes charges flow and transfer energy when it is connected in a circuit.
Discovery question
How can you make and store electricity?
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This activity uses hand generators and capacitors to make and store electricity.
Engage
We all use electrical power every day – lights, motors, computers, appliances, heat. It's a wonderful form of power because it can be used in so many ways. But where does it come from? How is it produced?
Name all the sources of electric power that you can think of.
ANSWER BOX
Find out the name of your local electric company. Go to the company website and find out where your electric power is generated and what sources of energy are used. Record what you found out below.
ANSWER BOX
Materials
- Genecon hand generator
- Voltage sensor
- Tokin capacitor
- AA 1.5 volt battery
- Holiday light
Explore
The Genecon hand generator has a magnet and coils of wire inside, just like a motor. When you turn the crank, the coils move through the magnetic field and push charges through a circuit. Huge generators that are run by water power operate just the same way!
Attach the Genecon to a holiday light. Light it up by cranking. Don't go too fast – you may burn out the bulb!
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While one person is cranking, have another person disconnect the Genecon from the light. What do you notice about the cranking?
ANSWER BOX
(answer: cranking suddenly becomes easier.)
A capacitor is a special device that stores electric charges. You can picture it as two plates that aren't connected, with extra positive charges on one side and negative charges on the other. When the two sides are connected in a circuit, the charges flow just like a battery.
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Connect the Genecon to the capacitor.
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Also connect the voltage sensor. Start collecting data.
NEED PHOTO
INSERT VOLTAGE DATA COLLECTOR
Crank the Genecon at least 20 times to charge up the capacitor. Then let the handle go. What happens?
ANSWER BOX
Describe the voltage graph.
ANSWER BOX
Clear and restart the voltage sensor. Crank the genecon again, but this time have one person disconnect the capacitor while another is cranking.
REPEAT VOLTAGE DATA COLLECTOR
Connect the holiday light across the capacitor. Keep it connected for at least 10 seconds. What happens? Why?
ANSWER BOX
(answer: the bulb lights, and gradually grows dimmer as the stored charge or energy is used up.)
Explain
Is it easier to crank the Genecon when it is connected to the light or when it is not connected?
o easier when connected
o easier when not connected
Why do you think this is true?
[very important scaffolding! When it's not connected, the Genecon isn't producing any energy or doing any work. When it is connected, the Genecon lights the bulb, which requires energy. The energy must be provided by the cranking, so the cranking is harder.
hint: think about energy.]
(answer: it is no longer transferring energy to the light, so it's easy to turn.)
What evidence did you observe that the capacitor can store electrical energy?
ANSWER BOX
Here is your graph of voltage when you charged the capacitor and then used it to light the bulb.
REPEAT VOLTAGE DATA COLLECTOR
Explain the changes in the graph in terms of energy. Hint: the voltage is a rough measure of the energy in the capacitor.
(this one is hard! )
What would happen to the voltage if you left the bulb connected for a long time?
ANSWER BOX
(answer: it would finally go back to zero when all the energy was transferred to the bulb.)
Elaborate
Charge up the capacitor again and disconnect it from the Genecon.
Connect the voltage sensor to the light bulb.
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Start collecting data. Light the bulb with the capacitor. Leave it connected for 20 seconds. Observe what happens.
Light the bulb with the AA battery. Leave it connected for 20 seconds. Observe what happens.
What is the difference between what the capacitor does and what the battery does?
ANSWER BOX
Why do you think they are different?
ANSWER BOX
Join up with another team. See if you can run one Genecon with another.
Crank one Genecon 10 times and record how many times the other one goes around.
ANSWER BOX
Why does the second Genecon go around fewer times than the first one?
ANSWER BOX
(answer: The system loses some energy as it is transferred from one Genecon to the other.)
Evaluate
In the Draw tool below, add the following labels to the circuit:
- mechanical energy input
- electrical energy transport
- electrical energy storage
DRAW TOOL WITH BACKGROUND: Cannot resolve external resource into attachment.
In the Draw tool below, add the following labels to the circuit:
- chemical energy input
- electrical energy transport
- light energy output
- heat energy output
DRAW TOOL WITH BACKGROUND: Cannot resolve external resource into attachment.
