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Electric Circuits

A closed loop through which current can flow.

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Burglar Alarm

Burglar Alarm


Credit: Philafrenzy
Source: http://commons.wikimedia.org/wiki/File:Beware_of_burglars._Police_notice_L.B._of_Barnet_30_June_2013.jpg
License: CC BY-NC 3.0

Many homeowners take steps to ensure that their home is not an easy target for burglars. How? They install a burglar alarm. Do you know a burglar alarm works? Both magnets and electric circuits are involved.

The Back Story

  • When a burglar alarm system is turned on, the alarm starts ringing loudly if a door is opened. Opening the door either closes or opens an electric circuit. This, in turn, causes the alarm to ring.
  • Credit: takomabibelot
    Source: http://www.flickr.com/photos/takomabibelot/2134214940/
    License: CC BY-NC 3.0

    Burglar alarm from the past [Figure2]


  • You can see how one type of burglar alarm works by watching this video of a middle school science fair project: 


Show What You Know

Learn more about burglar alarms by reading the first page at the link below. Then answer the questions that follow.

  1. Describe the science fair burglar alarm in the video above.
  2. Explain how the science fair burglar alarm works.
  3. Compare and contrast open-circuit and closed-circuit burglar alarms.
  4. Which type of alarm—open-circuit or closed-circuit—is the science fair alarm? What is a disadvantage of a closed-circuit alarm?
  5. Besides doorways, where can burglar alarms be installed?

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