show #1211


Insights &Connections



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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!


circuit a closed loop of conductors through which charges can flow

conductor a substance through which electrical charges can easily flow

current a flow of electrical charges

generator a device for producing electrical current by moving a coil of wire in a magnetic field

insulator a material through which electric charges cannot move

ion an atom that has gained or lost one or more electrons and is thus a charged particle

switch a device that closes or opens a circuit, thereby allowing or preventing current flow

voltage the pressure behind the flow of electrons in a circuit


Community resources

Local power utility


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


  • 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.


    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?


    Build an electromagnet using a D cell, a large steel nail, and about 50 cm (20") of insulated wire. Strip the insulation off two ends of the wire and carefully wrap the wire around the nail to form tight coils. Don't overlap the coils and make sure that you leave at least 6 cm (2.4") of wire free at each end. Connect the two ends of the wire to the two ends of the D cell and bring the tip of the nail very near some metal paper clips. The magnet will only attract if the circuit is complete.


    Examine your family's electric bill. What is a kilowatt? How much does the electric company charge for one kilowatt hour? Is that a constant rate? Make a list of the appliances that you think use the most electricity. Contact the electric company to see if you are correct. Does your family use the same amount of electricity each month? Why or why not?


    Static electricity can do more than make your socks stick together. You can use it to light a fluorescent tube. Get a small fluorescent bulb and a balloon. In a darkened room, rub the balloon on your hair a few times. Bring the charged balloon near one end of the bulb and you should see some light flashes.
    Newton's Apple is a production of KTCA Twin Cities Public Television. Made possible by a grant from 3M. Educational materials developed with the National Science Teachers Association.