What Happens when a Magnet Falls Through a Coil?

Iain Explains Signals, Systems, and Digital Comms

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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.
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Опубликовано:

2 янв 2022

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Комментарии : 54

@bonsaibywally 6 месяцев назад

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.

@iain_explains 6 месяцев назад

I'm glad it was helpful.

@fahad_hassan_92 Год назад

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

@iain_explains Год назад

It's great to hear that you found the video helpful.

@se2702 2 года назад

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!

@iain_explains 2 года назад

Glad it was helpful!

@mrinaldbhat9921 10 месяцев назад

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

@iain_explains 10 месяцев назад

Glad I could help!

@harryellis11 2 года назад

thanks for the video!

@iain_explains 2 года назад

My pleasure!

@sanjayd411 2 года назад

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

@iain_explains 2 года назад

Thanks. Happy New Year to you too! 😁

@emadibnalyaman8073 2 года назад

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

@hubercats 7 месяцев назад

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!

@arjunsnair4986 2 года назад

Happy new year sir

@iain_explains 2 года назад

Happy new year to you too. 😁

@stranger533 5 месяцев назад

❤so beneficial

@h7opolo 10 месяцев назад

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.

@crimzonsoulthebest6709 Месяц назад

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?

@znerol1 6 месяцев назад

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?

@iain_explains 6 месяцев назад

Connecting the ends of the coil with a wire wouldn't change the magnetic field effect on the magnet, since the only difference would be that charges would flow from one end of the coil to the other (through the connecting wire), rather than build up at the ends of the coil. Having excess charge at the end of the coil (or not) doesn't effect the magnetic field, since it is only the moving charges that effect the magnetic field.

@usmanrashid962 2 года назад

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).

@iain_explains 2 года назад

This case is discussed at the 8:40 min mark in the video. Ultimately the voltage/current returns to zero after the magnet has fallen far enough away from the coil.

@usmanrashid962 2 года назад

@@iain_explains Thanks

@gal766 5 месяцев назад

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?

@iain_explains 5 месяцев назад

First, it's important to point out that nothing ever moves "freely" - even if it is in deep space. Everything always has forces acting on it, from gravity, magnetic, and electrostatic. How it moves depends on the strength of those forces. Just because the magnet is inside the coil (in your question) doesn't mean the forces from above and below are equal in strength (or opposite in direction). Actually (although I didn't say it in the video) the force from the coils that are above the magnet, 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 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.

@gal766 5 месяцев назад

@@iain_explains First of all thank you for the response! I must have been tired that day, on the N side the field lines are in opposite directions, on the north side they are in the same direction, last time I taught that they where still opposing... And yes I know the meaning of free body, I used the world in the context not in its general meaning. Thank You.

@user-ow2kl9oz6e 5 дней назад

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

@Smmmile 2 года назад

Here's a nice video that shows how the Magnet Slows Down through a copper pipe: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-N7tIi71-AjA.html. The induced eddy currents in the pipe act in the same way to slow the motion of the magnet.

@iain_explains 2 года назад

Yes, exactly.

@Smmmile 2 года назад

@@iain_explains By the way the standard model of an EM Wave is always perpendicular E and B fields travelling through space. However they both seem to be in phase, where they both peak and trough in lock step. How can this be, if one causes the other, shouldn't there be some sort of lag between them somewhere? Cause and Effect so to speak. Perhaps a nice video for the future to explain. Cheers.

@georgestanciu5466 Год назад

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?

@iain_explains Год назад

Sorry, I'm not sure I understand your question. On a technical point, current flows "in" wires, not "from" wires. Current is the movement of electrons - so there needs to be a circuit for current to flow. Energy sources cause the current to flow (like batteries, or magnetic fields), and then the energy is dissipated when the current flows through circuit elements (such as resistors).

@georgestanciu5466 Год назад

@@iain_explains OK, you are right. Current flows in wires not "from". But where the electrons are coming from when the magnet passes true the coil? If the current flows true the coil - let's say - connected to a resistor.

@iain_explains Год назад

I'm not a physicist, but essentially the electrons that are moving are the ones that are already in the atoms that make up the metal wire. In metals, when a field is applied, the electrons disassociate from their protons, and move in the higher energy bands.

@georgestanciu5466 Год назад

@@iain_explains Exactly this is something that brings up the question: if they move into a higher state and leave the orbit then who will replace them? it may be a dumb question..

@mrinaldbhat9921 9 месяцев назад

@@georgestanciu5466 bro metals (the things used to make conducting wires) are electropositive, hence they are more than willing to give up and donate their electrons from their valence shell; implies when a magnet is brought near a coil (must be moving), the electrons in the metal atoms flow in a particular direction, and this direction will be such that it opposes the change in flux (flux is the magnetic field intensity through a given area, and is B.A (dot)) [Lenz' Law]. Hope this helped.

@ashutoshbhakuni303 Год назад

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?

@iain_explains Год назад

Not exactly. While the magnet is inside the tube, all of the coils _below_ the magnet are producing a magnetic field pointing up (slowing the magnet down, because the closest end of the magnet to those coils is the North end), and all of the coils _above_ the magnet are producing a magnetic field pointing down (which is also slowing the magnet, by pulling it up, because the closest end of the magnet to those coils is the South end). So while it is inside the tube, it is being slowed down "the most". The longer the tube, the more the magnet is slowed down, until it reaches an equilibrium speed. This is because, the slower the magnet moves, the weaker the current will be in the coil, and so the magnet will not actually stop/levitate. In a long tube, there'll be an equilibrium speed, that depends on the weight of the magnet, the number of coils, and how tightly they are wrapped.

@ashutoshbhakuni303 Год назад

Thanks!

@niyazigulnar56 3 месяца назад

I guess @ashutoshbhakuni is right. Your explanation@@iain_explains is correct for pipe since each pipe can be considered infinite number of independent circles wrapped. However, for coil, the coils are connected so when the magnet moves inside the pipe, the current will cancel out if the coil is long enough. This can also be observed experimentally. The magnet won't slow down as it falls inside a coil while it arrives at terminal velocity very fast in a pipe.

@razerh0 2 года назад

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.

@iain_explains 2 года назад

The answer to the overall question in your first paragraph is "yes". I pointed it to the left because I was visualising the part of the wire that was on the left hand side, coming out of the page towards me, and wrapping around to go back into the page on the right hand side. You are correct, the part of the wire on the right hand side would need my hand to be pointed the other way (as you say). Sorry, I'm not quite sure what your point is in your second paragraph.

@razerh0 2 года назад

@@iain_explains Does the angle of the wire when referring to the perpendicular component matter? What if the coil was wired, say, in the opposite direction? So instead of the wire coming around the back at the top of the coil, in started at the front of the coil and looking at it top down, it would curl clockwise? Would that change the direction of the induced current? My reason for asking this is if you only had information about one flux line, the one directly perpendicular from the front of the magnet, you would see a straight line "down the middle of the magnet". I understand if you're looking at flux lines on the "left" or "right side of a magnet, or "perpendicular" to the flux line itself, Oh okay, I think I just got it. The palm is basically the perpendicular component lol. One's hand must be in alignment with the direction of the direction of force of the flux line. 👍🏻 Got it ✋ I was looking at your drawing 2-dimensionally, instead of three. So I see where I was also wrong was that I was looking at this perpendicular component relationship between flux line and angle position of the wire. This is incorrect. The perpendicular component is the angle at which the flux lines leave from one pole of the magnet to the other.

@iain_explains 2 года назад

Great. I'm glad you understand it now. I tried to make my drawing look 3D, but I'm not the best artist, that's for sure. I'm glad you've found the video helpful.

@gabrielcotton4858 Год назад

@@iain_explains Thanks for this. Most explations of this seem to beat around the bush somewhat, Great video Iain! On Jaques' point, you may want to consider adding an annotation or something to say that the magnetic field vector is in the wrong direction. Considering the RH rule, if you viewed the solenoid from above, perpendicular B vectors would be pointing radially outwards. To visualise the correct direction on your diagram, draw a line from the coil centre to the choosen point. As i said this was a great video and I am not questioning your clear understanding of the topic but I can see how this small detail could cause further confusion.

@dalor4906 Год назад

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

@iain_explains Год назад

It's the _change_ in magnetic field that induces the current. If you have a constant stream of magnets, then there won't be a _change_ in magnetic field, and so there won't be a current.

@Handleitnow933 8 месяцев назад

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

@user-te9nb9dp6q Месяц назад

Thanks to you,l am now full understood.but l wanna know if you sir ,can transelet it into arabic .Again thanks for your help ❤

@BOBPortlandOr Год назад

Instead of a magnet dropped into a coil what happens if a doughnut magnet is dropped outside a coil.

@hushup8692 2 года назад

5 seconds in so no cheating. Atrophy should be the correct answer. I had a test in college on this.

@grahamgottard Год назад

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.

@x.its.tongue9784 8 месяцев назад

Subscribed! ~ BUT~ have done so many time before...... and ..... never yet to any avail. SO~ what I can't get my head around *** is *** ; 1] Why no information 'anywhere it seems ' on what happens WHEN~ a magnet spins 'within' a coil. 2] ~ 1 magnet.... N/S ~ top and bottom?~~~ Flat Bar type WITH also Disk type also round bar type 3]~ 1 magnet... N/S ~ sides Left & right?~~~ same types as above. 4]~ Series of magnets..... Flat, disk and bar ? 5]~ as above BUT with series set at 45 degrees to each other? ......... I will try to do so myself, BUT~ understanding what going on??? on clue, sorry very basic clue. 666]~ What happen when THE SAME is done within 2 coils SET apart by; a] 1cm b] 2cm etc, etc BUT coils arranged in same orientation c] Same but with coils arranged a 90 degrees to T'other AND 180 degrees as well as variations between. d] IF~ any result, what about 3 coils etc? ~ Please IF interested SHOW if possible VIA use of Magnet field Sheets, you know the green 1 currently supplied by 1st4magnets/UK. IF NOT interested PLEASE SAY SO........ right here. Time for me is NOW about 2-3yrs away. So short!