1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I need help with this electricty problem

  1. Dec 7, 2009 #1
    I need help with this electricty problem:(

    1. The problem statement, all variables and given/known data
    At the end of a long day, your instructor finally sits down to write your final examination, after making a cup of coffee he goes into his office, turns on the five, 40-Watt lights, and starts writing.

    How much current is flowing through the circuit in your instructor’ office?


    How many electrons are moving from the power company into your instructors’ home in order to continually generate the current in his office circuit?


    2. Relevant equations
    I can't find a formula to use to find current with just watts given.



    3. The attempt at a solution
     
  2. jcsd
  3. Dec 7, 2009 #2

    ojs

    User Avatar

    Re: I need help with this electricty problem:(

    Well, should we suppose the voltage is 120V or 230V (or something else)? Then you can figure out the electricity from the power equation for resistors (the tungsten thread in the lightbulb is essentially a resistor).
     
  4. Dec 7, 2009 #3
    Re: I need help with this electricty problem:(

    so 40W/230V=.179A?
     
  5. Dec 7, 2009 #4
    Re: I need help with this electricty problem:(

    would the .179 be multiplied by 5 because there are 5 lights?
     
  6. Dec 7, 2009 #5
    Re: I need help with this electricty problem:(

    Interesting question, what do you think? Say they are hooked up on individual circuits--answer seems obvious. What about if they were hooked up in series like ole fashioned Xmas tree lights?

    EDIT: BTW, unless you're in Europe, odds are the voltage is 120 or 110.
     
  7. Dec 7, 2009 #6
    Re: I need help with this electricty problem:(

    so it is 5* .173?
     
  8. Dec 7, 2009 #7
    Re: I need help with this electricty problem:(

    sure if you use 230V.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: I need help with this electricty problem
Loading...