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Resistance and DC circuit question

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  1. Apr 16, 2015 #1
    Here is the problem: I have already lost the ability to get the correct answer for A


    I
    1. The problem statement, all variables and given/known data
    28-p-007.gif
    (a) What is the maximum potential difference that can be applied to the terminals a and b?
    33.541 markSprite.png
    Which resistor will have the largest current? V

    (b) For the voltage determined in part (a), what is the power delivered to each resistor?
    resistor on the left W
    resistor at the top of the loop W
    resistor at the bottom of the loop W

    (c) What is the total power delivered to the combination of resistors?
    W

    2. Relevant equations:
    V=IR, P=IV, P=I^2R
    Resistors in series = R+R+R....
    Resistors in parallel (1/R)+(1/R)+(1/R).....



    3. The attempt at a solution
    My thought process was: If the max power to anyone resistor could be 22.5 watts then use P=IV, substitute the V for V=IR.
    My equation is now P=I^2R or 22.5W = I^2 (100Ω) => I = .4743 A for current at the resistor on side A. V=IR => V=.4743(100) => V=47.43

    I tried a similar method for the other side after consolidating the Resistors 1/100 + 1/100 = .2 => 1/.2 = 50. Basically a------100Ω--------50Ω--------b

    No **** just thought to add these to together and get a Reqiv. for the whole thing. So i just used the same method of P=I^2R to get a I = .3873.
    V=IR => 150Ω(.3873) = 58.095 V << Is this what you would get for part a? I don't really want to plug in answers yet for the problem if its wrong
     
  2. jcsd
  3. Apr 16, 2015 #2

    SammyS

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    Please state the complete problem.
     
  4. Apr 16, 2015 #3
    Three 100 Ω resistors are connected as shown in the figure. The maximum power that can safely be delivered to any one resistor is 22.5W.
    28-p-007.gif
    (a) What is the maximum potential difference that can be applied to the terminals a and b?
    33.541 markSprite.png
    Which resistor will have the largest current? V

    (b) For the voltage determined in part (a), what is the power delivered to each resistor?
    resistor on the left markSprite.png W
    resistor at the top of the loop W
    resistor at the bottom of the loop W

    (c) What is the total power delivered to the combination of resistors?
    W
     
  5. Apr 16, 2015 #4
    I apologize for not including that top part.
     
  6. Apr 16, 2015 #5

    SammyS

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    The resistor closest to point a can have a maximum current of approx. 0.4743 A.

    If the equivalent resistance is 150 Ω, what voltage is required to have a current of 0.4743 A ?
     
  7. Apr 16, 2015 #6
    Why do we use the equivalent resistance, but not the equivalent current that I found, was that an erroneous calculation?
     
  8. Apr 17, 2015 #7

    SammyS

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    Look at it another way.

    You can have at most 0.4743 A through the resistor on the left. Then how much current will flow through each of the two resistors that are in parallel?

    Assuming you get that right, what is the voltage drop across a & b ?
     
  9. Apr 18, 2015 #8

    RaulTheUCSCSlug

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    It helps to write down the certain rules for parallel and series circuits. When Voltage (potential difference) is the same, when does it change, when does the current change, when it is the same. When I did these questions back in high school, what helped was working the problems out with easier numbers and figuring out V,I,R, at different points in circuits.
     
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