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Behavior of a circuit when values increase or decrease

  1. Feb 16, 2010 #1
    1. The problem statement, all variables and given/known data
    Consider the behavior of the circuit, when various values increase or decrease.
    (Select I-increases, D-decreases, If the first is I and the rest D, enter IDDDDD).

    A) If R3 decreases, the current through R4 ___.
    B) If R3 decreases, the current from the battery ___.
    C) If R1 decreases, the current through R3 ___.
    D) If the voltage V decreases, the total current from the battery ___.
    E) If R1 decreases, the current through R6 ___.
    F) If R6 decreases, the power output from the battery ___.

    2. Relevant equations
    P = VI
    V = IR

    3. The attempt at a solution
    A) I = V/(R3+R4+R5) so if R3 decreases, the current through R4 increases
    B) If the current through R4 increases, the current through the battery decreases (conserved)
    C) increases (because current from R1 increases)
    D) V = IR, so if V decreases, I decreases
    E) increases (same as C)
    F) If R6 decreases, current increases, so power increases.

    So, IDIDII. But this is wrong, and I'm not sure which one I'm not understanding correctly. The diagram is attached!

    Attached Files:

  2. jcsd
  3. Feb 17, 2010 #2
    I don't know if this is correct. If you were to combine R3, R4 and R5 into one equivalent resistor, lowering R3 would lower the equivalent resistance, thus increasing current from the battery, so I think your part B is wrong. Although I could be wrong.
  4. Feb 17, 2010 #3
    I understand what you are saying, but I tried IIIDII, and it's still wrong, so I think i'm still missing something...
  5. Feb 17, 2010 #4
    Perhaps: If R3 decreases, more current would flow through R3, hence the current through R4 would decrease.
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