Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Shrinking Loop

  1. Mar 7, 2010 #1
    1. The problem statement, all variables and given/known data:
    A circular loop of flexible iron wire has an initial circumference of 166cm , but its circumference is decreasing at a constant rate of 13.0cm/s due to a tangential pull on the wire. The loop is in a constant uniform magnetic field of magnitude 1.00 T, which is oriented perpendicular to the plane of the loop.

    Question: Find the (magnitude of the) emf induced in the loop after exactly time 6.00 s has passed since the circumference of the loop started to decrease.

    2. Relevant equations:
    Flux= Close integral(B*dA)

    3. The attempt at a solution:
    C(t)=C0-at = 1.66-0.13(6.00)=0.88m
    0.88=2pi*r --> pi*r=0.44
    e=pi*rdrB = 0.44(1)(0.130m/s)/2pi = 0.00190V

    Since I am using web assign, it said this was incorrect. and gave me feedback which stated: A decrease in the circumference of the loop will also cause a decrease in the area and hence the magnetic flux. This will induce an emf in the loop.

    Hmm... seems like two things are chaning the circumference and the area. So where am I wrong, and what should I do?

    Edit: Also are there ways to enter integral sign and other things here?
    Last edited: Mar 7, 2010
  2. jcsd
  3. Mar 8, 2010 #2
    Anyone help on this?
  4. Mar 9, 2010 #3
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook