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Homework Help: Induced emf in triangle with changing area

  1. Mar 29, 2009 #1
    Two straight conducting rails form a right angle where their ends are joined. A conducting bar in contact with the rails starts at the vertex at time t = 0 and moves with a constant velocity of 7.00 m/s along them, as shown in Fig 31-44. A magnetic field with B = 0.350 T is directed out of the page.


    (a) Calculate the flux through the triangle formed by the rails and bar at t = 2.50 s

    (b) Calculate the magnitude of the emf around the triangle at that time.

    (c) If we write the emf as E = at[tex]^{}n[/tex], where a and n are constants, what is the value of n?


    Alright, I can figure this out, only I don't know how to find the rate of change of the length of the two non-moving bars. With that, I could find the area at t = 2.50 s, and the change of the magnetic flux, and I could muddle through the last one ;)
  2. jcsd
  3. Mar 29, 2009 #2


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    Add a vertical line in the center of the diagram, from the point where the rails join to the moving bar. You do know the rate of change of this length. Can you express other sides in terms of this length?
  4. Mar 30, 2009 #3
    Oh, I see. The height would be vt, and the base would be 2 times the height... Thank you
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