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Electric Circuits

A closed loop through which current can flow.

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How Can You Resist?

How Can You Resist?


Credit: Tylercat5
Source: http://commons.wikimedia.org/wiki/File:MV_Lamp_175_W.JPG
License: CC BY-NC 3.0

Do you see the small blue and silver cylinder near the bottom of this mercury-vapor light bulb? It’s an electrical device called a resistor.

The Back Story

  • A resistor is a device used to regulate the amount of electric current in a circuit. Resistors are used in light bulbs and appliances to limit the amount of current that reaches them. They work by resisting the flow of current through the circuit.
  • Credit: US CPSC
    Source: http://www.flickr.com/photos/uscpsc/8723105569/
    License: CC BY-NC 3.0

    Electric heaters use resistance to generate heat instead of light [Figure2]


  • Resistors come in different sizes. Which size does a device need? You can use Ohm’s law to find out.
  • Ohm’s law states the relationship among voltage, current, and resistance in a simple electric circuit. For a better understanding of these relationships, experiment with this applet: http://www.physics.uoguelph.ca/phyjlh/Fendt/phe/ohmslaw.htm

Can You Apply It?

At the link below, learn more about Ohm’s law and how to use it. Then answer the questions that follow.

  1. State Ohm’s law and represent it with a formula.
  2. What SI units are used for the variables in the formula for resistance in question 1?
  3. How many ohms of resistance does a resistor need to provide for a 12-volt circuit to carry 6 amps of current?
  4. How much current does a 120-volt circuit carry if it contains a resistor that provides 10 ohms of resistance?
  5. What do you think might happen to an appliance in a circuit if the wrong resistor is used so the appliance gets too much current?

Image Attributions

  1. [1]^ Credit: Tylercat5; Source: http://commons.wikimedia.org/wiki/File:MV_Lamp_175_W.JPG; License: CC BY-NC 3.0
  2. [2]^ Credit: US CPSC; Source: http://www.flickr.com/photos/uscpsc/8723105569/; License: CC BY-NC 3.0

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