Find the light bulbs and four toggle switches. Make sure all of the switches are "OFF" and try turning the generator pulley slowly. While continuing to turn the pulley slowly, turn any one of the switches "ON" and see if you notice any change.
The exhibit only works well with only one switch at a time "ON." If more than one switch is on, it is unlikely you will light the bulbs.
The easiest bulb to light is controlled by the switch furthest from the generator. Turn that switch "ON" and make sure the other three switches are "OFF." Turn the pulley faster, until the bulb shows light. Try generating electricity one at a time through the second switch, then the third, then the fourth.
See if you can discover which bulb is easiest to light.
The black cylinder is a direct current or DC motor that is being used as a generator to make electricity. Inside the case is a permanent magnet. Inside the permanent magnet's field is a coil of wire. When you turn the pulley you are causing the coil of wire to move within the magnetic field. These three "ingredients" create electricity.
When all four switches are "OFF" electricity is not flowing and the pulley is easy to turn. When any switch is turned "ON" you are pushing electricity through the wire and bulb - the increased resistance you feel in the pulley is the effort needed to push electricity.
The 1 AMP bulb is the easiest to light.
In a flashlight, the energy needed to produce light is stored in batteries. Once the batteries are used up (empty) they have to be replaced. Some bicycles have generators to make electricity for front and back lights. The bicycle tire rubs against and turns the generator pulley. The bicycle rider is supplying the energy to create the electricity.
Many science books describe how one can build a very small generator using a long piece of very fine wire, a permanent magnet and a small light bulb.
Why isn't electricity free?
As you found out, it takes work or energy to make electricity, so there is a cost to make it. Expensive equipment is needed to build the generators. Very expensive wires, utility poles, transformers, and other equipment is needed to bring the electricity from the generators to your home. Finally, many people are needed to keep the equipment working, repair storm and other damage, keep track of bills and payments and many other activities.
Can you identify the energy transformations that took place, starting with the energy in sunlight, when you were lighting a bulb? How efficient is this series of transformations?
Sunlight was transformed into wheat, corn, milk and other foods. Your body transformed the foods you ate into chemical energy and stored it. When you turned the pulley that stored energy was converted into mechanical energy (movement of your arm) which in rotated the pulley and generator shaft. That motion then was transformed inside the generator into electricity.
There is waste in each transformation of energy. Some of the wheat is destroyed or lost during harvesting. You might not have eaten all of your breakfast this morning and threw the remainder away. While turning the pulley, your arm encounters some wind resistance and perhaps some friction with your clothing.
Is energy conserved when you are turning the pulley and all of the switches are "OFF?" How is the energy conserved that causes the bulb to light?
When all of the switches are "OFF" the pulley is very easy to turn, so little energy is being applied. There is some friction in the bearings for the generator shaft and some wind resistance. The energy being applied is being transformed to heat energy.
When a bulb is being lighted, more energy is being put into turning the pulley. This energy is being transformed into heat, due to friction in the wires as the electricity is flowing; into light energy given off by the bulb; and into heat energy, also being given off by the bulb. Producing light from this type of bulb, called an incandescent bulb, is very inefficient because of the amount of heat energy given off by the bulb.
Would installing a larger diameter pulley on the generator shaft allow you to generate more electricity?
Electricity is created as the generator's shaft rotates. One revolution of the pulley corresponds to one revolution of the shaft. A larger diameter pulley would mean that your hand travels a further distance to produce one revolution of the shaft. A smaller diameter pulley would allow you to increase the number of revolutions per minute or RPM of the generator shaft.
Would it be cheaper to purchase a pedal powered generator and use it for some low energy uses in the home, such as listening to a radio or watching television? How would you prove your answer?
Not likely. To prove your answer, determine how much less electricity you would have to purchase, and the cost per unit of electricity. Compare that to the cost of the generator and maintenance.
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This exhibit is described in the Exploratorium Cookbook series.
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