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!

Rate of change of the magnetic field

  1. Jul 26, 2009 #1
    1. The problem statement, all variables and given/known data
    The resistance of the loop is 0.55 Ω. At what rate the magnetic field strength increasing or decreasing? (a=8.4 cm, I=148 mA. Give answer in T/s.)
    The loop is a square, so all the distances around are a=8.4 cm


    2. Relevant equations
    dI=AdB
    dI=rate of change of the flux
    A=area
    B=magnetic field




    3. The attempt at a solution

    I found V by using Ohm's Law V=IR, which is the same as emf

    but now I am lost, I feel like I need to find B, obvious reasons. Do I just use the equation

    B=Uo*N*I/2R

    N=1 because only 1 loop
    Uo= constant
    I=current
    R=radius, so half of a?
     
  2. jcsd
  3. Jul 26, 2009 #2
    I am still lost, no matter how I go about solving this I seem to be missing 1 or 2 bits of information..... usually B is one of those.
     
  4. Jul 26, 2009 #3

    diazona

    User Avatar
    Homework Helper

    Okay, let me restate this:
    Does that accurately describe what the problem is asking?

    If so, you do have enough information. Figuring out the EMF was a good first step, but now you need an equation that relates that EMF to magnetic flux. Do you know what it is?

    (your B=Uo*N*I/2R is not the right equation for this problem)
     
  5. Jul 27, 2009 #4
    EMF=N(dI/dt)

    dI is delta flux?
     
  6. Jul 27, 2009 #5

    diazona

    User Avatar
    Homework Helper

    Yep, that's it. But note that nobody really uses I for flux. Normally the formula would be written
    [tex]\varepsilon = N \frac{\mathrm{d}\Phi}{\mathrm{d}t}[/tex]
     
  7. Jul 27, 2009 #6
    right, I just didnt know how to right Phi on the computer
     
  8. Jul 27, 2009 #7

    diazona

    User Avatar
    Homework Helper

    Some people have signatures with the Greek letters that you can copy and paste from. There are other ways too, depending on what operating system you're using.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Rate of change of the magnetic field
Loading...