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: Help with test review problem, magnetic field/capacitors

  1. Mar 28, 2004 #1
    Alright, my teacher gave us a review sheet of problems for the test tomorrow, supposedly all the concepts will be covered on the test, and I've got NO CLUE where to even start on this problem. It supposedly has something to do with section 30.7 in Serway/Beichner's physics text, titled "Displacement Current And The General Form Of Ampere's Law", but I can't find anything in there or elsewhere that helps me understand this.
    A .4A current is charging a capacitor that has circular plates 13cm in radius.
    (a) If the plate separation is 4.00 mm, what is the time rate of increase of electric field between the plates?
    (b) What is the magnitude of the magnetic field between the plates 5.00 cm from the center?

    I can't find any equations relating capicitor charging with magnetic fields, or vice versa... help? Please? I'm on my knees here! :frown:
  2. jcsd
  3. Mar 28, 2004 #2

    Doc Al

    User Avatar

    Staff: Mentor

    I don't have that text, but I find that hard to believe, given the title of the section! :rolleyes:
    In a nutshell, the idea is that the changing electric field within the capacitor creates the magnetic field.

    You need to apply Ampere's law to find the magnetic field inside the capacitor. But first you have to understand Maxwell's extension of Ampere's law to include the so-called displacement current. This displacement current is proportional to the rate of change of the electric flux. The book should have this, but if not, here's a start:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook