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: Inducing a magnetic field with a wire due to flux

  1. Aug 5, 2011 #1
    1. The problem statement, all variables and given/known data
    A stationary loop of wire is placed in a magnetic field directed into the page. The current in the loop of wire:

    and then it lists 4 multiple choice options. the answer is: the current in the loop of wire is clockwise if the magnetic field is decreasing.

    2. Relevant equations
    non really

    3. The attempt at a solution

    My issue is when trying to solve this i realized that if the current is clockwise then a magnetic field will be created that is going into the page. BUT lenz's law states the induced current will create a magnetic field OPPOSING the inducing magnetic field.

    So I would have answered the question by saying the current would be counterclockwise since this would make a magnetic field that comes out of the page (i.e. opposing the inducing magnetic field)

    I'm not sure why the answer is the one that is written. Any help is appreciated.
  2. jcsd
  3. Aug 6, 2011 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Welcome to PF.
    Not quite. The induced current creates a field opposing the change in the inducing magnetic field.

    The inducing field is into the page, but decreasing. Therefore the change in this field is in what direction?
  4. Aug 7, 2011 #3
    The change is "out of the page" thus the created field opposes this by going into the page!

    Thanks so much!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook