Electric Circuits

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Author: Marc Rosner

With some materials scrounged from the basement or attic and a few dollars' investment, you can model typical electric circuits and make new designs of your own. If you make any good inventions, patent them and sell your ideas!

Thomas Edison (1847-1931) searched for years to find the best materials and methods for manufacturing lightbulbs. One of the best designs, tungsten filaments in a vacuum or in a noble gas, is still used today.


  • wire strippers
  • insulated wire (copper phone line, old lamp cord, or speaker wire)
  • metric ruler
  • power supply (6-volt lantern battery, or power supply from an old external computer modem or answering machine)
  • electronic components with screw terminals (minilight fixtures and doorbells)
  • several wire nuts
  • electric tape
  • other assorted components: lowvoltage (3-to-12-voIt) lightbulbs, single- and double-throw knife switches (single-pole), doorbell button, buzzers, LEOs, small electric motors, photosensitive resistors (available at hardware stores or RadioShack)
  • test equipment: ampmeter and voltmeter, or multitester (available at RadioShack)


To Assemble the Components

  1. Use wire strippers to remove the insulation and expose the bare wire. If your wire is a bundle of smaller wires, remove the outer insulation first. Sometimes you can make a small cut and pull an inner wire along the incision, tearing the insulation open. The insulation falls away, exposing the inner wires. Then cut the single strands to workable lengths—20 cm is a good length—and strip 1 to 2 cm of insulation off each end.
  2. Read the power supply specifications and see what it delivers. The input should be 120 volts (V) AC, plugging into your wall. The output should be 5 to 15V DC, 100 to 500 milliamps current. An amp (ampere) is a unit of electric current, and a volt is a unit of electrical potential difference and electromotive force. If you think of an electric current as water flowing in a hose, the amount of water is the amperage, and the speed of the water is the voltage. To find out why amperage kills, and voltage doesn't, see the next chapter.
  3. Electric Circuits

  4. Components that have screw terminals, such as minilight fixtures or doorbells are useful. You connect a wire to other components and wires by wrapping it around the terminal screw and tightening it, by twisting the two wires together. The exposed connections can be covered by twisting them on a wire nut or wrapping them with electric tape.
  5. Use low-voltage bulbs (3 to 12V) matched as closely to your power supply as possible. It's easier to work with bulbs if you have fixtures you screw them into, with screw terminals. Get some knife switches or doorbell buttons. Knife switches come in different types—a couple of single- and double-throw switches will suffice. You can mix and match other components, such as buzzers, light-emitting diodes, (LEOs), motors, and photosensitive resistors. Amp- and voltmeters are useful test equipment to determine the current and voltage present in the circuit.

To Build and Test Circuits

  1. Get to know the symbols here as you build each circuit. Once you learn how to read circuit diagrams and build from them, you can use these symbols to design new circuits before handlingthe equipment.
  2. Electric Circuits

    1. Circuit 1 is a simple circuit with a power supply, two wires, and a bulb. Each terminal of the bulb leads to one terminal of the power supply. The bulb goes on when the circuit is completed. To turn the bulb off, disconnect one wire from the power supply.
    2. Electric Circuits

    3. Circuit 2 has two bulbs in a series circuit. Each bulb will be about half as bright as the bulb in circuit 1 because the voltage is split between the two bulbs. The electric current passes successively through each component.
    4. Use a voltmeter and ampmeter (or a multitester, both meters in the same device) to analyze series and parallel circuits.
    5. Circuit 3 has two bulbs in a parallel circuit. Both bulbs receive the full voltage and should be as bright as the bulb in circuit 1. The electric current divides into two paths and rejoins.
    6. Circuit 4 has a single-pole, single-throw knife switch for turning a bulb on and off.
    7. Circuit 5 has a single-pole, double-throw knife switch that can be used to turn on one bulb or the other.
    8. Don't look at circuit 6 yet. It's a fun one to try to design yourself: a two-location light switch with two single-pole, double-throw knife switches. Imagine a stairway with one light. From two locations (with a switch at each location), such as the upper floor and the lower floor, you can turn the bulb on if it's off, or off if it's on, regardless of the position of the other switch. After you've built this circuit, can you make a three-location switch?
  3. Now you're ready to build, and test, other circuits of your own design.


Awesome Experiments in Electricity and Magnetism by Michael Dispezio (New York: Sterling, 2000).

Benjamin Franklin's Adventures with Electricity (Science Stories series) by Beverley Birch (Hauppauge, N.Y.: Barron's Juveniles, 1996).

Blinkers and Buzzers: Building and Experimenting with Electricity and Magnetism by Bernie Zubrowski (Topeka, Kans.: Econo-Clad Books, 1999).

Electricity and Magnetism (Making Science Work series) by Terry Jennings (Orlando, Fla.: Raintree/Steck Vaughn, 1998).

The Thomas Edison Book of Easy and Incredible Experiments by James G. Cook (New York: John Wiley & Sons, 1988).

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