# Falling wire in a B field

1. Mar 27, 2008

### pcandrepair

1. The problem statement, all variables and given/known data

A U-shaped conducting rail that is oriented vertically in a horizontal magnetic field. The rail has no electric resistance and does not move. A slide wire with mass m = 10 g, L = 0.45 m, and resistance R = 0.10 Ω can slide up and down without friction while maintaining electrical contact with the rail. A magnetic field of B = 1.5 T is perpendicular to the rail as shown. Determine the terminal velocity (in m/s) of the slide wire if it is released from rest and falls under the force of gravity.

2. Relevant equations

F(B field) = I*(L x B)
F=mg
Induced motional emf = -B*L*v
Magnetic flux = B*L*x (with x being the other length of the rectangle which is (in this case) always changing)

3. The attempt at a solution

I am stuck on how to start this one. I'm pretty sure I have to find either the induced emf or the induced current. Then I could find the force of the magnetic field pushing up (against gravity) on the wire. Maybe? Any help on how to start this would be greatly appreciated! Thanks!

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