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Finding Frictional force from the magnetic equation Fb=BIL

  1. May 6, 2013 #1
    1. Calculate the frictional force of a crossbar sliding at a constant velocity on two railings. Answer. 1.26 N

    Given, Crossbar= 256 Ω
    Distance (separation of railings)= .35 m
    V (Setup connected to battery)= 12 V
    B (Magnetic field)= 1.2 T

    2. Fb= BIL

    3. The only thing that makes sense would be to do is divide (12 v/ 256Ω) to find I. And then substitute Fb = (1.2 T)(12v/256Ω)(.35 m). But the answer I get is .02 N. Nowhere near the given answer, anything I could be missing??
  2. jcsd
  3. May 6, 2013 #2

    rude man

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    Homework Helper
    Gold Member

    I also computed 0.02N.

    No point in taking the counter-emf into account, either. That would just further reduce the computed frictional force, plus we aren't given the velocity anyway.
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