![]() ![]() You can imagine it's a cylinder that can roll to the right, and the magnitude of it's velocity, we're going to say is lowercase 'v'. Is this loop that we have, This right part of the loop is movable. The magnitude of the magnetic field at any point of the I have a magnetic field that is constant, and it's going straight out Where would that energy come from to do that? A tiny push would send the rod zooming off. You would give the rod a little push, and then that force would push it some more in the same direction, and then the rod would go faster so that force would get bigger, so the rod would go faster, etc etc etc. Think about what would happen if somehow the force was in the same direction as the velocity. If that person stops pushing, the opposing force will cause the rod to come to rest. But why should force be needed to keep the rod moving at constant velocity? It must be that there's an opposing force that the person doing the pushing has to fight against. For that person to be doing work, they have to be exerting force in the direction that the rod is moving. Where does it come from? Whoever is pushing the rod. If charge is moving, somehow energy is getting put into that system. ![]() This makes sense because energy has to be conserved. That means it has to, in this case, try to make the bar stop moving. There's more than one way to do it, but the easy way is to use Lenz' law, which tells us that the induced EMF will oppose the change that is creating it. ![]()
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