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hy23
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Homework Statement
A circuit is formed by an aluminum bar that can slide along two (parallel) metal rails which are joined by a battery. There is a magnetic field which passes through the circuit. The battery also has an internal resistance of r. Everything else has ~no resistance. When the circuit is closed, battery sends current around the circuit.
Show that the aluminum bar reaches a terminal velocity.
Homework Equations
[tex]\epsilon[/tex]=Blv
[tex]\epsilon[/tex]=emf
v=velocity
l=length of aluminum bar
B=magnetic field
The Attempt at a Solution
At first inspection it seems like the answer is straightforward...v=[tex]\epsilon[/tex]/Bl
but I doubt it's that easy and after thinking about it I'm very confused.
So this is what made me confused: the battery sends a current through the aluminum bar, and the magnetic field then exerts a magnetic force on the aluminum bar, making it slide along the rails, but then this increases the magnetic flux through the circuit, so then a current opposing the battery current must be induced...but then wouldn't the currents cancel out and no movement occur?
Also in a short circuit, is the terminal voltage 0?
Since [tex]\epsilon[/tex]-IR=V
and I=[tex]\epsilon[/tex]/R