# Induced EMF from moving conducting rod

#### OhBoy

1. Homework Statement
Lets say we have two horizontal rails connected by a resistor to the left, and we have a movable conducting rod that slides without friction on the rails.There is a uniform magnetic field going into the page.

2. Homework Equations
F = ILB

3. The Attempt at a Solution
Now, I know that if the rail moves to the right with a velocity v, then Hall's effect shows that there will be an induced emf, and the resistor will draw a current. Now there should be a resisting force to stop the rod from moving but I'm not sure where the force comes from. If there is a current going counter clockwise, the current through the bridge will provide its own magnetic field going out of the page. Now, going back to the rod, current is moving up, field from bridge out of the screen, that makes the force going towards the right, not the left to resist the velocity. Do I use the field into the pay because it will (always?) be stronger than one produced by current through resistor? That would make the force to the left. I just want to make sure I have a conceptual understanding of where this force comes from.

So what am I doing wrong? Where is the resisting force derived when a force goes in to move the conducting rod?

Last edited:
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#### TSny

Homework Helper
Gold Member
Do I use the field into the pay [page] because it will (always?) be stronger than one produced by current through resistor? That would make the force to the left. I just want to make sure I have a conceptual understanding of where this force comes from.
Yes, in this situation it is generally assumed that the field produced by the induced current is negligible compared to the fixed external field (directed into the page).

"Induced EMF from moving conducting rod"

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