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Issue finding change in voltage across a resistor

  1. Apr 6, 2014 #1
    1. The problem statement, all variables and given/known data

    Determine the voltage drop across R1
    R1 = 770 , R2 = 630 , and R3 = 470 .
    The equivalent resistance is 816Ω

    19-39alt.gif


    2. Relevant equations

    V = IR


    3. The attempt at a solution

    1.) I find the total current of the circuit:

    V = IR -> I = V/R
    I = 12v/816Ω = 0.015A

    2.) I then find the voltage drop across that particular resistor:

    V = IR
    V = 0.015A * 770Ω
    V = 11.32v

    This has been confirmed to be the wrong answer.

    I don't understand what I am doing incorrectly.

    Could someone please help me understand my mistake (where ever it may be)?

    Many Thanks!
     
  2. jcsd
  3. Apr 6, 2014 #2

    phinds

    User Avatar
    Gold Member
    2016 Award

    You need to draw the circuit with all of the voltages and currents labeled so that you can see clearly what is going on. Thinking that the 15ma all goes through R1 is incorrect.
     
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