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 Field Change for Induced Current of Loop

  1. Feb 21, 2012 #1
    1. The problem statement, all variables and given/known data

    A single conducting loop of wire has an area of 8.0×10−2 m^2 and a resistance of 110 Ω. Perpendicular to the plane of the loop is a magnetic field of strength 0.37 T.

    At what rate (in T/s) must this field change if the induced current in the loop is to be 0.33 A?

    2. Relevant equations

    Trying to solve for ΔB/Δt

    3. The attempt at a solution

    We have a change in magnetic flux, but it seems to be due to ΔB rather than ΔA, so Δflux = ΔB*Acosθ (However since cos(90) = 0, I'm not sure if this will be correct).

    Using Faraday's Law |ε| = N|(Δflux/Δt)|
    Substituted Δflux = ΔB*A into Faraday's Law --> ε = N(ΔB*A/Δt)
    Substituted the equation for the induced EMF into I = |ε|/R and solved for ΔB/Δt
    ΔB/Δt = I*R/A (N=1 because the loop has 1 turn)

    453.75 T/s = (.33A)*(110Ω)/(8.0*10^-2 m^2)
    asks for 2 significant digits -> 450 T/s = Final Answer

    I'm not sure where I'm going wrong...
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Feb 21, 2012 #2
    θ would not be 90 as Area vector and B make 0 angle
     
  4. Feb 21, 2012 #3
    Okay, then cos(0) = 1, which would prove that my assumption Δflux = ΔB*A*cos(0) = Δflux = ΔB*A

    How does the rest of my thought process look?
     
  5. Feb 21, 2012 #4
    as as i know you are doing correctly ,
    where are you stuck ?
     
  6. Feb 21, 2012 #5
    Mastering Physics tells me this is the wrong answer, though it does not give any explanation as to why.
     
  7. Feb 21, 2012 #6
    what is " mastering physics "
     
  8. Feb 21, 2012 #7
    It's the online website for our physics homework. When you enter your answer, you are told whether or not your answer is correct. You are given 5 attempts, during which the points you earn diminish.
     
  9. Feb 21, 2012 #8
    Even I am in confusion as they have given magnitude of magnetic field
    (which means a constant field ) but asking find at what rate it would vary
     
  10. Feb 21, 2012 #9
    Yes, I noticed this as well. I purposely left that out of my equation as we are attempting to solve for ΔB/Δt. I assume it's the authors of the homework trying to trick us into thinking the value is necessary. Though I cannot see how it could be.
     
  11. Feb 21, 2012 #10
    I am sorry as I fail to help you further with this problem
     
  12. Feb 21, 2012 #11
    You know the resistance of the loop and you know the current so you should be able to find the induced emf
     
  13. Feb 21, 2012 #12
    "I am sorry as I fail to help you further with this problem "

    Thanks, Kushan. I appreciate your help. I think there might be an issue with the website. It wouldn't be the first time.

    Technician: You might notice that is exactly what I attempted to do... No worries though.
     
  14. Feb 21, 2012 #13
    As it turns out, the website wanted a different number of significant figures. Albeit, an incorrect number with the given information...
     
  15. Feb 22, 2012 #14
    Thank god
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?