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Headlight Power Question

  1. Aug 24, 2013 #1
    1. The problem statement, all variables and given/known data
    The headlights on a car operate typically at 60 W and the parking lights typically at 5 W. Assuming that there are two main headlights and four parking lights, what length of time will it take to discharge a 60 Ah battery, if the lights are left on?


    2. Relevant equations
    I = Q/t

    V = W/Q

    P = W/t

    P = I2*R

    P = V2/R

    P = IV

    3. The attempt at a solution
    I have gotten no where with this question. :frown:

    All that I could do was find that the total power consumed by the lights:

    PT = (2*10) + (4*5) = 140 W

    , and the charge of the battery:

    1 Ah = 3600 C
    ∴ 60 Ah = 216,000 C

    , and that's it.

    I have tried simultaneous equations by substitution and elimination but that doesn't work because all of the equations are derived from the base equations I = Q/t, V = W/Q and P = W/t, so I end up getting P = P all the time.

    Hint's anybody?

    Thank you.
     
  2. jcsd
  3. Aug 24, 2013 #2

    TSny

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    Gold Member

    Not sure, but maybe you are suppose to assume that the voltage of the battery is the typical voltage for a car battery.
     
  4. Aug 24, 2013 #3

    ehild

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    Gold Member

    You need the voltage of the car battery to find the current. Look at Automotive battery - Wikipedia, the free encyclopedia, or just see the battery in your car...

    ehild

     
  5. Aug 25, 2013 #4
    Hmm... It seems like it... Based on this link, which is the worked solution to the question.

    Thank you TSny and ehild.

    So much for "complex, challenging and novel"... :rolleyes:
     
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