What Happens when a Magnet Falls Through a Coil?

Explains the Electromagnetic interactions that happen when a magnet is dropped into a coil of metal, and why it causes the magnet's falling speed to slow down.

Also, something I should have mentioned in the video, it is worth pointing out that the force from the coils that are above the magnet (when the magnet is inside the tube), actually pull the magnet up! This is because the induced magnetic field lines (induced by the coils above the magnet) point down inside the coil. Which effectively means the coils above the magnet are acting as a North Pole magnet - which has the effect of attracting (up) the South Pole that is at the top of the falling magnet.

[wallygrandpa]

at least someone who explains the whole way through the coil. I was looking for that for quite some time as everyone explains what happens when the magnet goes towards and away the coil but never while it's inside the coil.

[fahad_hassan_]

Brilliant analysis, finally I can understand this clearly after half an hour of searching through other videos.

[se]

Hi Iain! I love this analysis. Video gave me insight as to what is really going on that I had not considered previously. You show complex things in a simple fashion. I appreciate that -thanks!

[hopolo]

funny how the induction is a result of the coiled, insulated wire versus the eddy currents and counter-emf if the tunnel is shorted, i.e., a copper pipe. i wonder how much electricity and/or counter-emf would result if a coil of insulated wire is wrapped around a copper pipe, with the insulation removed from the wire where it makes contact with the pipe. the magnet would induce eddy currents in the pipe which should be absorbed by the wire, thus adding electricity to the induced current, but the wire is shorted to the pipe so the current would flow along the length of the pipe inside the coil, and then to the terminals. this should possibly decrease the counter-emf, making the magnets fall faster than if the coil were absent, and resulting in lower current than if the pipe were not present. thus, this arrangement cancels the hindrance to movement of a magnet inside a conductive material.

[mrinaldbhat]

awesome! I didn't have a clear picture before watching this, and now you have solved my problem; keep up the great work!

[crapulence.]

hey man, could you just tell why the graph didnt not increase linearly, i was doing some questions of resic halliey, the question was what happens to the current when a bar magnet passes through a singular coil, im confused if the graph will increase linearly or like a sinusoidal graph

[hubercats]

Another really helpful video. Thank you! I recently tried dropping a rectangular Neodymium magnet (poles on the long, wide sides) and found that there was no slowing of the magnet (Note that the copper pipe was just slightly larger than the narrow dimensions of my magnet). I wish I were as skilled as you with vectors but I’m guessing that the result I observed makes sense on account of the magnet’s field being horizontal vice vertically oriented. Does this result make sense? Thanks again!

[crimzonsoulthebest]

Dr. what will happen if I let the coil be horizontal instead of vertical position, and the magnet passing by the coil vertically, will there be a change in flux, thus induced current?

[razerh]

I don't quite get how at 3:44, you've decided that the perpendicular component is to the left. Why is it to the left? Why is it not to the right? I understand the thumbs up part, because the wire is moving upward relative to the position of the magnet. However you could just very well have pointed your hand to the right. I'm not understanding the perpendicular component.
The wire is perpendicular to the field exiting out of the magnet. Is it because you have used the reference of the N to S flux line on the left side of the magnet, that determines the direction of the perpendicular?
Is it true that if you drew the N to S flux line on the right hand side of the magnet that you would then point your hand to the right instead and find the current being induced "into the page"? My analysis proves yes on concordance with the direction you have indicated.

Skipping ahead of 7:11, it would seem better to call it an acute angle component 🤔
At 90degree it could go either left or right. However given the direct of the flux outward to inward from the right hand side to the left, at that outer point to the left relative to the magnet in the middle, the measurement of the right hand rule is that the induced current goes into the page, because of the acute angle direction of the magnetic flux line to S from N.
My point is that the direction of the flux line tends to move in the direction that is less than 90degree at the point where there is a perpendicular component.

[usmanrashid]

Hello;
I, ve got an question that if an bar magnet is allowed to fall through an coil connected to either the galvanometer of ammeter what will be the deflection shown when the Bar magnet falls away from the coil. (Given that the Magnet falls with N Direction Below).

[grahamgottard]

The area under the voltage-time graph represents the change in Flux (phi) linking the coil. E = - d phi/ dt, so phi = integral E dt... ie the area between the curve and the time.axis. the area under the initial pulse should.equal.the area under the second pulse.
The entry pulse of emf should be a low V for a long t, the departure pulse is a high V for a short t. With equal.areas.

[emadibnalyaman]

Thank you very much, can you plz use some Matlab examples especially on the communications lecture if you can it will be great.

[znerol]

Hi Iain, thanks for this clear explanantion. I would be interested to know if in your example the coil wires would be connected to create a (short)circuit or open, what would the difference be?

[gal]

When it goes in the pipe it creates a force that oppose the magnet direction, when it goes out the force pushes the magnet out, so, when it is in the middle of the pipe, when the voltage is zero, why does both forces don't cancel out and it just moves freely?

[ashutoshbhakuni]

If the coil is long, when magnet is inside the current shud b zero, so no slowing down? The positive and negative voltages are for entry and exit. So a long solenoid would cause a different response compared to magnet falling in a copper tube?

[georgestanciu]

Excellent explanation of back emf. I have a question if you can answer will be great: from where is coming the electricity in the coil over and over again?
I ask that because if the current (in the generator - coil) is flowing "from the wire" as they told us on physics then why this flow never ends?

[ToyMarston]

Maybe attach magnet to tuning fork and put coil around it and put it in outer #space, wouldn't that vibrate nearly forever ?

[sanjayd]

Fantastic as always! HNY to you sir!🙏👍👍👍

[dalor]

If you released magnets through the coils at the proper rate wouldn't you make DC current?

[Handleitnow]

Is the energy field harming or does it repel harmful fields such as WiFi?