Electricity

 

Overview

David conducts a study of electrical circuits. Segment length: 9:01 When it comes to understanding electricity, to get to the heart of the matter you must literally get to the heart of matter--the atom. Atoms are the building blocks of matter and they are composed of three particle types. The central core of the atom is called the nucleus and it contains positively charged particles called protons and neutral particles called neutrons. The movement of many charged particles in the same direction is called an electric current. Charged particles flow most easily through conductors, such as metals, or through some liquids, such as salt water. Electrons in metals are loosely attached to the atoms, so they can move easily. The human body (which is mostly salt water) is also a good conductor, which is why electric shocks can be so dangerous. Insulators, on the other hand, do not conduct electricity well. Their electrons are tightly bound to their atoms and do not move easily. Typical insulators include rubber, wood, glass, and most plastics. Electricity will only flow when a power source, such as a battery or a generator, sets the electrons in motion and when the electrons can complete a full circle. Consider this example--electrons flow from a battery down a wire to a light bulb, through the filament of the bulb, and then back up another wire to the battery. This closed loop is called a circuit. No electrical device, whether it's a simple flashlight or a complex computer, will work unless the circuit that delivers the electric current is a complete loop. Electricity becomes dangerous to you when you become part of the electrical loop--when the electrons have enough energy and make adequate contact to pass through your body. You can touch both ends of a flashlight battery and feel nothing, but if you're wet and in contact with household electricity, water can make a very good path through your skin and your body, making you part of the electrical circuit! Electrical energy always seeks the shortest route around the circuit back to the source, which in the above example is the battery. If the wires both touch a conductor, such as a metal tabletop, the electrons will take that shorter route back to the battery, rather than travel to the light bulb. (Conveniently, scientists call this a "short circuit.") So why don't birds get electrocuted when they sit on power lines? The power lines that are suspended in pairs between power poles are analogous to the wires that run between the battery and the light bulb. As long as birds sit on only one, they offer no "shortcut" to complete the circuit. But if their wings accidently touch both adjacent power lines, the electrons take a new path and complete the circuit through the unfortunate bird's body!

• Imagine a world without electrical power. How would you cook, clean, and entertain yourself?
• Even though electrical energy is useful, its production often causes environmental problems. Acid precipitation from burning coal and disposal of nuclear waste are just two of them. What are some alternative power sources and how can conservation help minimize the damage?

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Activity

Which common objects are insulators and which are conductors? To test it for yourself, you can build a simple, battery-powered conductivity tester.

MAIN ACTIVITY

flashlight with one fresh D cell

3 pieces of insulated wire, each approximately 15 cm (6") long with the ends stripped

roll of masking or duct tape

penny

comb

several pieces of fabric

metal fork or spoon

several different rocks

various objects for testing

1. To build your tester, unscrew the top of the flashlight which has the bulb assembly in it. Take one wire and tape it to the metal tip of the light bulb and tape a second wire to the metal ring that touches the side of the bulb.
2. Tape the other end of the wire connected to the tip of the light bulb to the (+) end of a D cell and touch the free end of the second wire to the (-) end of the cell. The light should go on because you have completed a circuit. If it doesn't, make sure all the connections are taped tightly and make good contact.
3. Tape one end of the third wire to the (-) end of the cell and touch its free end to the free end of the wire coming from the bulb holder. Again, the light should go on. Try touching the two free ends of the wires to the penny at the same time. The bulb should light because the penny is made of copper, a good conductor.
4. Collect your objects to be tested and predict if they are insulators or conductors. Then try them out with your tester.

   Questions

   1. In general, what types of materials make the best conductors?
   2. Look inside the body of the flashlight. How does the switch control make the light go on and off?

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Resources

• Math, I. (1981) Wires and watts. New York: Charles Scribner's Sons.
  
• Nye, B. (1993) Big blast of science. New York: Addison-Wesley.
  
• Stanley, L. (1980) Easy-to-make electric gadgets. New York: Harvey House.
  
• 3-2-1 Classroom Contact videotape: Generating Electricity. GPN: (800) 228-4630.
  
• VanCleave, J. (1991) Physics for every kid. New York: John Wiley Publishers.
  
• Vogt, G. (1986) Generating electricity. New York: Franklin Watts Publishing.
  
• Williams, J. (1992) Projects with electricity. Milwaukee: Gareth Stevens Children's
  Books.

Community resources

Local power utility

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