Unit: Energy and Control- Electricity

 Some fish use electricity to stun their prey. The most famous is the electric eel which can produce more than 500 volts of electricity! This is enough to stun an animal as large as a human. Special muscle cells on each side of the fish, called electroplaques, create and discharge the electricity in a series of bursts, each lasting only 1/500 th of a second. The electric eel lives in the muddy rivers of the Amazon basin in South America.

 What we need: A lemon A clean, shiny copper penny A nail A compass 1m of wire

 Neatly wrap 1m of thin wire lightly around a compass 4 or 5 times. Leave the wire ends loose. This is your electricity detector.  Push a clean, shiny penny and nail into a lemon. Place them next to each other but make sure they do not touch each other.  Touch one end of the wire from step 1 to the penny and the other end to the nail.  Watch what happens to the compass needle  Try the same experiment using an apple, a potato, or a jar of vinegar.

 Draw a labeled diagram of your lemon circuit.  What kind of energy transformation occurs when the lemon makes electricity?  Did you try this experiment with another fruit, a vegetable, or vinegar. What happened?  What do you think would happen if you connected many lemon “batteries” in a series?

 Research to find out about one of the following sources of electricity: hydro-electric, nuclear, fossil fuels (coal, oil, and natural gas), solar, wind, tidal, and geothermal.  Write a report about the source of energy you selected. Explain how electricity is produced from the source. Present your report to the class or make an interesting display. Make sure you include if the source of electricity is renewable or not.

 In the late 1700s, 2 Italian scientists experiments with producing electricity from chemicals. They were Luigi Galvani, and Alessandro Volta. Galvani discovered that electric current stimulated the nerves in a frog’s leg. Volta built the first battery called a voltaic pile. The battery consisted of copper and zinc disks, piled one on top of the other. Discs of leather soaked in salt water were placed between the metal disks. Within the pile, an electric charge was produced as electrons flowed through the slat water from the copper to the zinc. Volta described this electric flow to a current similar to water flowing in a rive. Today we use the word “volt” to measure electrical energy.

 Producing electricity from a lemon is very similar to using a voltaic pile. The salt water in the pile causes electrons to flow from the copper disks to the zinc disks. Inside the lemon, the acid juice causes the electrons to flow from the copper penny to the iron nail. The lemon current, however, is very week and can only be detected from the compass needle. You would need to connect many lemons in series to light up a light bulb.

 A modern battery works in the same way as your lemon battery. The core of the battery is a carbon rod. It is surrounded by a chemical base. The outer case of the battery is zinc. The chemical paste causes electrons to flow from the electrons from the zinc to the carbon rod when the battery is connected to a circuit. A battery transforms chemical energy to electric energy.

 Electricity in a wire causes a flowing magnetic field. A compass needle detects the electric current because the needle is magnetized. It moves slightly when an electric current passes through the wire.

 Electric generators produce electricity in a totally different way. Generators usually transform mechanical energy into electric energy. Michael Faraday developed the first generator in He generated electricity using the force of electromagnetism. Electromagnetism transforms mechanical energy into electrical energy when a coil of copper wire is rotated near magnets.

 The electricity in your home and school is produced by huge generators that are rotated by using steam or falling water. Hydroelectric generating stations transform the gravitational energy of falling water into electrical energy.  Falling water is a renewable resource, an energy resource that can be used over and over again. The sun (solar power) and the wind are other examples of renewable resources that are used to generate electricity.

 Most other generating stations use a fuel (oil, coal, natural gas, or uranium) to heat water and turn it into steam. As the steam expands, it turns the generator, making electricity. But coal, oil, natural gas, and uranium are non- renewable resources- energy resources that can only be used once. Once these resources are used up that’s it! They’re gone! It takes millions of years for the earth to produce resources such as coal and oil.