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 from a Graph?

  1. Mar 9, 2007 #1

    candyq27

    User Avatar

    1. The problem statement, all variables and given/known data
    I have a graph of an emf of a generator vs time, and i know the cross-sectional area per turn is 0.03m^2 and there are 160 turns. From the wave graph I figured out the frequency of the generator is 2.4Hz and the angular speed is 14.96rad/s. I need to figure out the magnetic field.


    2. Relevant equations
    e=-NAcos0B/t


    3. The attempt at a solution

    I found the frequency and angular speed from the graph but I have no idea how to find the magnetic field from a graph. Please help. Thank you.
     
    candyq27, Mar 9, 2007
  2. jcsd
    Phys.org - latest science and technology news stories on Phys.org
  3. Mar 10, 2007 #2

    dobry_den

    User Avatar

    It's important to realise that the emf is directly proportional to the change of magnetic flux:

    [tex]\Phi = BS\cos{\omega}t[/tex]

    [tex] emf = -N \frac{d\Phi}{dt}[/tex],

    that is:

    [tex] emf = -NBS \frac{d}{dt}\cos{\omega}t = -NBS\omega\sin{\omega}t[/tex]

    Then rearrange it to get the formula for B.
     
    Last edited: Mar 10, 2007
    dobry_den, Mar 10, 2007
  4. Mar 10, 2007 #3

    candyq27

    User Avatar

    Ok so I rearranged the formula to get B=emf/-NAwsinwt
    = 28/(-160)(.03)(14.96)(sin(14.96*.315))
    =28/71.808
    =0.38993
    Is that correct? Thanks!
     
    candyq27, Mar 10, 2007
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook