Finding Frictional force from the magnetic equation Fb=BIL

[aldoftybg]

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
V=IR



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??

 

[rude man]

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.