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Current across a resistor

  1. Jun 26, 2010 #1
    1. The problem statement, all variables and given/known data
    Number 15
    [PLAIN]http://lookpic.com/d2/i2/386/kFYE2mOH.jpeg [Broken]
    http://lookpic.com/d2/i2/386/kFYE2mOH.jpeg [Broken]

    2. Relevant equations
    Rs=R1+R2+R3
    Rpar=1/r1+1/r2+1/r3
    I=V/R



    3. The attempt at a solution
    1/(1/5+1/10+1/5)=2
    Rtotal=7
    I=21/7
    I=3

    I don't know what else to do to solve this problem. Any help would be greatly appreciated.
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Jun 26, 2010 #2

    berkeman

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    Staff: Mentor

    Welcome to the PF.

    That's a good start. Once yuu figure out the parallel resistance of those 3 resistors, use the voltage divider equation to tell you what the voltage is across the 3 parallel resistors. that will then give you the current through that individual 10 Ohm resistor leg.

    And the current is "through" the resistor. Voltages are across resistors, and currents flow through resistors.
     
    Last edited by a moderator: May 4, 2017
  4. Jun 26, 2010 #3

    vela

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    Staff Emeritus
    Science Advisor
    Homework Helper
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    When you applied Ohm's law, you used V=21 V, which is the voltage across the entire combination of resistors, and R=7 ohms, which is the equivalent resistance of the entire combination, so the current I you found is the current that flows through that equivalent resistance.

    What you're asked to find, however, is the current through just the 10-ohm resistor. One way to do that is apply Ohm's law to that individual resistor, and to do that, you need to find the voltage drop across the resistor, which you can find by applying Kirchoff's voltage law.
     
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