# Conducting rod is free to move over a loop under influence of B field?

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

The conducting rod ab shown in the figure (Figure 1) makes contact with metal rails ca and db. The apparatus is in a uniform magnetic field 0.800 T, perpendicular to the plane of the figure.

If the resistance of the circuit abdc is 1.50 Ω (assumed to be constant), find the magnitude of the force required to keep the rod moving to the right with a constant speed of 7.50 m/s . You can ignore friction.

I’ve already found that (if the rod moves with constant velocity 7.5 m/s) the EMF is 3 volts.

**2. Relevant equations**

F = qv x B

V = IR

q = It

**3. The attempt at a solution**

I thought I could somehow use ohms law to find the charge q i needed in the equation for the Lorenz Force by q = I t, but I don’t have a t. I don’t really know where to start solving this one. :confused:

http://ift.tt/1lTWelb

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