How to use an ac power meter

Lesson 2

#2 of 6 TITLE: HOW TO USE AN AC POWER METER

 

SUMMARY:  Students learn how to use a plug in the wall power meter with the permission and supervision of an adult. 

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Instruction

  1.  Right a grant / get funding to purchase some of these low cost plug in the wall style power meters.  They are about $15.00  each.  Click here for purchase information.

  2. Go over the following with your students:

    1. Safety instructions provided in the owner's manual / instructions that come with the power meter

    2. The basic formula for power which is Volts x Amps = Watts

    3. Instruct the students on how to use the different display modes described in documentation that came with the power meter

  3. Get a 25 Watt bulb from the store.  Also get a bulb to plug adapter to use.

  4. Now you use an AC power meter to measure the AC voltage coming out of the wall.  It should be some where around 120 Volts AC.  NOTE: You are responsible for reading the volt meter manual safety precautions!!   But in short, you verify that your AC volt meter has an AC voltage range able to accommodate 120 Volts AC,  set the voltage meter to AC voltage (MAKE SURE It's not set to AMPS), and stick the probes into the wall outlet.  It's easy.  Just don't touch the metal parts of the probes.

  5. Now that you have measured the exact voltage level of your class room outlet, tell the students to right down this as a constant to use in their formula for power. 

  6. Have the students  right down how many Amps the 25 Watt Bulb is drawing on their work sheet.  NOTE: If you use more than 25 Watts, you run the risk of some one touching the bulb and getting burnt!!

  7. Now have them multiply the voltage you measured from the outlet, times the current measured by the power meter, and calculate how much difference there is between the power indicated by the power meter and what was calculated by using the formula. 

  8. Wrap up with a discussion with having different lab / student teams report out on what they observed.