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Homework Help: EMF in magentic field

  1. Jan 20, 2009 #1
    See question below:

    http://img140.imageshack.us/img140/479/30680788kr3.th.jpg [Broken]

    In order to calculate the EMF, the markscheme using the formula "E=Blv", the markscheme uses the linear speed of point M. Can someone please explain why this is the case - I understand the derivation of E=Blv, just not why the linear speed at M is used.

    I used a different method (I calculated the area/second and multiplied it by B), however I would be interested to know how the method above manifests itself.

    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Jan 20, 2009 #2
    Work out what v is by using by using speed equals circumference of circle divided by t.It gives the same answer as your method but your method is better.
  4. Jan 20, 2009 #3
    So why is the midpoint, M used?

  5. Jan 20, 2009 #4
    Think of one of the radial lines of length l which is rotating.The velocity of this(and all the other lines)varies from zero at the centre to a maximum at the end.When we use Blv we should take the average velocity which is at the midpoint M.I still prefer your method.
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