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Homework Help: Voltage Drop over Constant Current Circuit

  1. Feb 22, 2012 #1
    1. The problem statement, all variables and given/known data
    So I have a problem that I am working on that requires me to find the voltage drop across a 1000 mA current source, and two 2000Ω resistors that are in parallel. I've added a picture of a circuit diagram for this below.

    2. Relevant equations

    V = I * R

    3. The attempt at a solution

    I am not particularly familiar with how constant current power supplies work, but from my understanding, as opposed to a regular battery, current sources push a constant current throughout the entire circuit, and have variable voltage to accommodate different resistances it passes through. So, for the question above, I would think that you could just use ohm's law to solve for the voltage correct? For example, since the resistors are in series, you add them together to find total resistance:

    Rtotal = R1 + R2....

    Rtotal = 2000Ω + 2000Ω

    Rtotal = 4000Ω

    We know the current is at 1000mA, so:

    V = I * R1
    V = I * R2

    V = 1A * 2000Ω = 2000V

    Am i doing this correctly, or am I not thinking it through right?....

    Also, how would I find the Voltage going through the current source itself?

    Thank you for any and all answers. New to these boards but have glanced at other problems on here throughout the past couple quarters. This is seriously an invaluable resource.

    Attached Files:

  2. jcsd
  3. Feb 22, 2012 #2
    Are you getting 2000 v across battery?
  4. Feb 22, 2012 #3
  5. Feb 22, 2012 #4


    User Avatar

    Staff: Mentor

    That's about right.
    That's the voltage across each resistor. So voltage across both must be 4000V.
    The current source provides the voltage that you measure across the two resistors. So the voltage across the current source = the voltage across the combined resistances.

    When describing voltage across a circuit element, it is usually a good idea to point out which end is more positive than the other, too. Given that current is flowing into the resistor string from the left and emerging from the right, which end must have the higher potential?
  6. Feb 22, 2012 #5
    Totally meant in series. I have basically the same problem but them in parallel as well, so I got mixed up when typing it out. Thanks though!

    That makes sense since the voltage should drop from its initial (from the power source) to zero after it passes through the resistors so it should just be the the sum of the voltages through each resistor as you said. Thank you so much for your help! I knew it had to be a fairly simply problem, I was just getting tripped up by the fact that it was a current source as opposed to a regular battery that produces constant voltage.

    Thanks everyone!
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