Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Average Current Simple

  1. Feb 6, 2008 #1
    Average Current...Simple....

    1. The problem statement, all variables and given/known data
    A typical American family uses 1430 kWh of electricity a month.
    What is the average current in the 110 V power line to the house?

    2. Relevant equations

    3. The attempt at a solution
    Don't I just change kWh to W and divide it by the voltage...
    1430 x10^3 = 1430000 / 110 = 13,000A which is def. not right lol.
  2. jcsd
  3. Feb 6, 2008 #2
    Well, [itex][\text{kW}\cdot\text{h}][/itex] is not the same thing as a kW, which you can convert to W. Instead, [itex][\text{kW}\cdot\text{h}][/itex] is power (kW) multiplied by time (h), which is energy. You have the equation right (i.e. E = iV), but you need to convert to the SI unit of energy, the joule. How would you do that?
  4. Feb 6, 2008 #3
    Do 1430x10^3 * 3600s = 5.148x10^9 J
  5. Feb 6, 2008 #4
    but what now?
  6. Feb 6, 2008 #5
    You had the right idea before with your equation E = iV. You know E, you know V, so you can find i.
  7. Feb 6, 2008 #6
    but what is E? Its not measured in J?
  8. Feb 6, 2008 #7
    Sorry, that is my mistake. I'm not thinking very clearly today. Power is iV, so you are right to be confused. You know that she uses 1430 kWh in a month. You can find out how many seconds are in a month, and figure out the average power, in kW or W. Then you divide by voltage to find the current.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook