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Homework Help: Enery phisic question

  1. Nov 11, 2005 #1
    hi here is the question

    A 60 watt light bulb is left swithed on for 10 hours. If the light bulb is 15% effcient, calculate the amount of light energy produced in that time. what is the total energy consumption of the light bulb in this time.

    so i need to find work done right so is that power divided by time to get the energy and then find 15% of that am i right i am bathed by this.
     
  2. jcsd
  3. Nov 11, 2005 #2

    Kurdt

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    A watt is 1 unit of energy per unit time. You know how much of the energy was turned into light (15%) and the length of time the light was left on. No need to introduce work.
     
  4. Nov 11, 2005 #3
    so do i divide watts by time taken?
     
  5. Nov 11, 2005 #4
    so 60 watts divided by10 hours which is 6 15% of 6 is 0.9 if i am correct

    can you please tell me if i am right if not can you advive me where i went wrong
     
  6. Nov 11, 2005 #5

    Kurdt

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    your answer is incorrect. First you need to think about units
    watts is per second whereas you're given a time in hours. Secondly do you think the energy would be lower or higher than how much you are using in one second?
     
  7. Nov 11, 2005 #6
    so 10 hours is 600 minutes 36000 seconds and 60 watts goes goes in in 36000 2160000 so 15% 324000 am i right
     
  8. Nov 11, 2005 #7

    Kurdt

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    Correct. now remember to state you units. energy is measured in.....
     
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