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Calculate the resistance, then find the current at the new voltage

  1. Oct 3, 2005 #1
    A 78.9 W, 107.3 V light bulb is plugged into a 59.2 V outlet. If energy costs 4.9 cents/kW*h, how much does it cost per month (30 days) to leave the light bulb turned on? Answer in units of cents.

    This is what I did:

    (78.9W/107.3V)(59.2V)(24hours)(30days)(4.9cents/kW*h)(1kW/1000W)

    I got 153.58 cents. I know the answer is incorrect, but where did I go wrong?
     
    Last edited by a moderator: Jan 7, 2014
  2. jcsd
  3. Oct 3, 2005 #2
    P=VI
    V=IR

    Calculate the resistance, then find the current at the new voltage. Then use conversion factors to get your price.
     
  4. Oct 3, 2005 #3
    Thanks, that helped!
     
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