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Homework Help: Resistance with circuit

  1. Aug 15, 2010 #1
    1. The problem statement, all variables and given/known data
    Three 60 w 120 V bulbs are connected to a 120 V battery. 2 Bulbs are in parallel with each other in a smaller loop. The third is in series with the battery and the other loop.
    find voltage difference across bulb three.

    2. Relevant equations
    R= V^2/P
    1/R_loop= 1/R_1

    3. The attempt at a solution

    1/R_total = 2/240 R_total= 120 +240 =360

    I _total = V/R = 120/360
  2. jcsd
  3. Aug 15, 2010 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    Start by finding the total circiut resistance.

    You must have RT= RB+ RL

    RB is the resistance of a single bulb and
    RL is the resistance of the parallel pair of bulbs.

    RL is :

    [tex] \frac 1 {R_L} = \frac 1 {R_B} + \frac 1 {R_B} [/tex]

    So RL = .5 Rb

    Now you should be able to complete the problem on your own.
  4. Aug 15, 2010 #3
    I got V_3 is .33A * 240 = 80v but its -80v b/c its loosing right?
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