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I'm a bit unsure about the concept of a magnet being dropped through a conductive metal tube. I know that the change in flux will induce eddy currents in the walls of the tube which will resist the motion of the magnet. However, is the magnitude of this resistive force equal to gravity, ie. resulting in the magnet falling at a constant speed?

Otherwise, does the magnet still accelerate inside the tube and when it exits, is it faster or slower than when it entered?

Wilo
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1 Answers1

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You can anticipate that for small velocities, the resistive force is proportional to velocity. This is because the eddy currents are proportional to a single time derivative from Faraday’s law in the quasistatic limit. Thus, just as for Stokes’ drag in a viscous fluid, the magnet accelerates until the force cancels velocity. You can calculate the terminal velocity if you calculate the prefactor in the resistive force.

Hope this helps.

LPZ
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