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Circuits, what am I doing wrong

  1. Apr 14, 2010 #1
    1. The problem statement, all variables and given/known data
    [PLAIN]http://img258.imageshack.us/img258/9067/39943009.png [Broken]

    given this circuit if each of the resistors may consume maximum power = 24 W without overheating, find the maximum power that the circuit can consume


    2. Relevant equations
    P = I*V
    V=I*R


    3. The attempt at a solution
    ok the first two are in parallel, so i found the resistance of both, which is 3/2, then we have two resistors in series and I found the total resistance which is 3/2 + 3 = 9/2

    before doing this i found the I(total)

    which is P = I*V => 24 = I^2*3 => I = +/- 4

    having the I total and the total resistance I said

    P = I^2*R = 16*9/2 = 72 W

    but the book says 36, what am I doing wrong?

    Thanks
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Apr 14, 2010 #2
    You are wrong with your first statement. You said that the max. power consumption of a SINGLE resistor is 24W, but calculated a power consumption of a whole circuit.

    My idea is as it follows:
    1. P=I^2*R. Obviously the currency flowing through the resistor on the right will be the, khem, biggest (dunno what's the proper word in english :P). You should assume that it is 24W. It allows you to calculate the currency, and then everything else. Checked, gives 36W.

    E: Due to the rules of the board I've deleted the exact solution :).
     
    Last edited: Apr 14, 2010
  4. Apr 14, 2010 #3
    thanks irycio I understand it now
     
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