Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: First order Circuit

  1. Nov 17, 2012 #1
    I'm not sure what happens when you replace the inductor with a short circuit. The current source is what throws me off.

    One thought I had was that you can remove the 6 and 2 kohm resistors, but then I don't know what ahppens to the current source.
  2. jcsd
  3. Nov 17, 2012 #2
    Everything you've said is right. The voltage across the inductor being 0 also means some current is flowing through the 3k resistor. The current source demands a certain current flow, so KCL should give you the inductor's steady current.
  4. Nov 17, 2012 #3
    So then are you saying that you remove the current source as well since the voltage around it is zero?
  5. Nov 17, 2012 #4
    The question is designed to trick your intuition. A current source can pull any amount of current no matter what the voltage across it is, including 0 volts.

    What you've said about the 2k and 6k resistors is correct -- the voltage across them is zero so Ohm's law gives zero current through them. The current source continues to draw 5mA no matter what.
    Last edited: Nov 17, 2012
  6. Nov 17, 2012 #5
    Ok, so then you're saying that there is 2mA of current traveling up [i(0) = -2] through the inductor?
  7. Nov 17, 2012 #6
    Yes, that's it.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook