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dishwasher95
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- TL;DR Summary
- If a magnet is dropped through a copper tube, the magnet will travel slower towards the ground than if there was no tube at all. I understand the principle of why this is happening but I don't know how to calculate an exact value for the size of the braking force (in Newtons) that is acting upon the magnet as it falls through the copper tube. Is there a simple way of doing this?
I want to know how to calculate the braking force acting on a magnet falling through a copper tube.
The setup can be seen in this video (YouTube, @ 1:49 - 3:12): Copper's Surprising Reaction to Strong Magnets.
Note that it's not a copper tube in the video but a plastic tube surrounded by a copper wire (this doesn't matter as the same physical principles apply).
In the video, a magnet is dropped through a coil of copper wire, resulting in current going through the wire (when the circuit is closed) which generates a magnetic field opposing the magnetic field of the magnet falling through the coil.
How do I calculate the size of of the braking force? Or rather; how do I calculate the strength of the generated magnetic field in the coil?
Bonus question: Why does the magnet fall easily through the coil when the LED light is connected to the circuit?
I'm assuming it's because the resistance is increased in the circuit, meaning less current is passing through the coil, meaning a weaker opposing magnetic field is generated? Is this correct?
But then when the magnet is moving faster through the coil (where the LED is attached), shouldn't more voltage (EMF) be generated? Leading to more current?
Some equations that I have in mind:
Ohm's Law: V = R * I
(V = voltage [V], R = resistance [Ohm], I = current [A])
emf = B * v * l
(emf = electromotive force [V], B = strength of magnetic field [Tesla], v = relative velocity between magnetic field and copper wire [m/s], l = length of copper wire in the magnetic field [m])
Alright I think that's it - let me know if I should clarify anything.
Thanks!
The setup can be seen in this video (YouTube, @ 1:49 - 3:12): Copper's Surprising Reaction to Strong Magnets.
Note that it's not a copper tube in the video but a plastic tube surrounded by a copper wire (this doesn't matter as the same physical principles apply).
In the video, a magnet is dropped through a coil of copper wire, resulting in current going through the wire (when the circuit is closed) which generates a magnetic field opposing the magnetic field of the magnet falling through the coil.
How do I calculate the size of of the braking force? Or rather; how do I calculate the strength of the generated magnetic field in the coil?
Bonus question: Why does the magnet fall easily through the coil when the LED light is connected to the circuit?
I'm assuming it's because the resistance is increased in the circuit, meaning less current is passing through the coil, meaning a weaker opposing magnetic field is generated? Is this correct?
But then when the magnet is moving faster through the coil (where the LED is attached), shouldn't more voltage (EMF) be generated? Leading to more current?
Some equations that I have in mind:
Ohm's Law: V = R * I
(V = voltage [V], R = resistance [Ohm], I = current [A])
emf = B * v * l
(emf = electromotive force [V], B = strength of magnetic field [Tesla], v = relative velocity between magnetic field and copper wire [m/s], l = length of copper wire in the magnetic field [m])
Alright I think that's it - let me know if I should clarify anything.
Thanks!