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Homework Help: Voltage and current calculation on a mixed circuit

  1. Nov 23, 2008 #1
    1. The problem statement, all variables and given/known data
    I have the following circuit

    R1 = 22 ohm, R2 = 39, R3 = 82, R4 = 100,R5 = 10
    and V = 2volt

    I'm asked to calculate the voltage and current over de resistors

    when the switch is open and when the switch is closed

    2. Relevant equations
    when 2 resistors form a combination the current is the same and V = IR

    when 2 resistors are in parallell there voltages are the same and Ii = V/Ri

    3. The attempt at a solution
    well when the switch is open I obtain the following
    the resistors R1 and R4 form a combination and so do R2 and R3 the voltage remains equal for both combinations so we can easily calculate the current
    I1=I4 = 2v/(22+100)ohm = 0.016 A
    now we find the voltage over both resistors
    V1= 0.016 * 22 = 0.361 Volt
    v4 = 0.016 * 100
    Same way for I2 and I3

    But I'm stuck when the switch is closed how do I calculate the current and voltage then ?
  2. jcsd
  3. Nov 23, 2008 #2


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    It might be well to read up on "Delta-Wye" transformations.
  4. Nov 23, 2008 #3


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    Staff: Mentor

    Have you learned how to write KCL equations yet? Write the two KCL equations for the left and right nodes, and solve for the two unknowns V(left node) and V(right node).
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