1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Kirchhoff's loop rule problem

  1. Apr 24, 2008 #1
    1. The problem statement, all variables and given/known data
    Read the image. I was always confused about this. Is Kirchhoff's loop rule here:

    [tex]-L\frac{dI}{dt}+IR = 0 [/tex]


    [tex] L\frac{dI}{dt}+IR = 0 [/tex]

    . Please explain your answer carefully.

    2. Relevant equations

    3. The attempt at a solution

    Attached Files:

  2. jcsd
  3. Apr 24, 2008 #2


    User Avatar

    Staff: Mentor

  4. Apr 24, 2008 #3
    Well what they do in the second link is use the given fact that the current is increasing to decide what the sign must be. But the same equation should hold whether the current is increasing or decreasing. How do you decide which of my equations to use without knowing whether the current is increasing or decreasing through the inductor?

    BTW, the do we know the current is decreasing here? Why?

    I don't mean to be rude, but can you help me with this specific example?
    Last edited: Apr 24, 2008
  5. Apr 25, 2008 #4


    User Avatar
    Science Advisor
    Homework Helper

    please show YOUR attempt to solve this first.

    explain YOUR thoughts carefully, then someone might help you.
  6. Apr 25, 2008 #5
    say we go clockwise around the smaller loop starting from S and record the voltage changes as we go around. How do we get the sign of the first voltage change?
  7. Apr 25, 2008 #6


    User Avatar

    Staff: Mentor

    The battery establishes an initial potential. When the switch has been set for a long time, it means that it has reached a steady-state situation, i.e. the current is constant, which means di(t)/dt = ?

    However there is a current and stored energy in the inductor. There is also a voltage drop across the resistor, and only across the inductor when current is changing.

    If the battery is by passed, i.e. short-circuited, what then happens to the current?
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Kirchhoff's loop rule problem
  1. Kirchhoff's rules (Replies: 1)

  2. Kirchoff's Loop Rule (Replies: 8)

  3. Korkhoff's loop rule (Replies: 1)