1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Magnetic Field in Capacitor

  1. Jan 2, 2015 #1
    1. The problem statement, all variables and given/known data

    A cylindrical parallel plate capacitor of radius R is discharged by an external current I. The
    total electric field flux inside the capacitor changes at a rate dΦe/dt = I/ ε0. What is the
    strength of the resulting magnetic field B(r, I) inside the capacitor at a radial distance r
    from the centre axis? Start the answer with Maxwell’s extension to Ampere’s law.

    2. Relevant equations

    So using the line integral ∫B⋅dl= μ0 (I + Id )

    3. The attempt at a solution

    you get B⋅2πr= μ0 (I + Id )

    However i don't understand what I and Id are?

    I have the equation Id= ε0e/dt

    however i don't understand why this is true or where this takes me?
  2. jcsd
  3. Jan 3, 2015 #2

    rude man

    User Avatar
    Homework Helper
    Gold Member

    You have an equation and you don't know what the symbols represent? May I suggest your first step is to find that out.
    (Hint: the problem tells you what I is; it's given.)
    Last edited: Jan 3, 2015
  4. Jan 3, 2015 #3
    Sorry i should have qualified, I know what the symbols represent, and i realize that I_d is given, i also assume I is 0. However what i don't understand is why?
  5. Jan 3, 2015 #4

    rude man

    User Avatar
    Homework Helper
    Gold Member

    Actually, I is given, not Id. I is the current in the wiring, not inside the capacitor. Inside the capacitor, I = 0 as you say.
    Your answer is to be B(I,r).
    Do you know the Maxwellian extension of Ampere's law? It relates the circulation of B to the electric flux inside the circulation perimeter.
    Hint: the perimeter is itself a function of r. It is inside the circular plates.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted