Shakeable Dynamo Part 3: How electromagnetic induction works

Atoms of a magnet

[ad#Google links]

Shakeable Dynamo Part 1: Why bother?
Shakeable Dynamo Part 2: Building the initial dynamo

Right, so we’ve built the initial alternator/ dynamo and it works, not amazingly, but it works and we need to make this is a little bit more robust and protect all those lovely windings as well, at the same time we also need to convert our alternating current (AC) and convert that to direct current (DC), so that we can use this to power a small circuit/ LED without it turning on and off all the time. First I should probably explain how this all works… (feel free to correct me if I am wrong in my assumptions)

How do magnets work?

Atoms of a magnetEvery magnet creates a magnetic field due to the arrangement of the atoms in the material, in very simple terms, the atoms are spun so that most of the electrons are on one side of the atom, creating a negative charge on one side, while the lack of electrons on the other side of the atom exposes the positive charge of the protons in the nuclei. In the very simplified diagram to the left, the  nuclei are blue and the electrons are orange and their arrangement produces the  different overall charges with more electrons flowing to one end of the magnet. This also explains why when you cut a magnet in half you will get 2 magnets, not a separate south and a north pole. This then creates the polarisation effect we see in magnets and this is also where naming conventions jump into confuse matters! So first of all magnets are referred to has having a ‘north’ and a ‘south’ pole due to this polarisation effect from the different atomic charges. This is because when suspended freely, the magnets ‘north end’ will spin to point to the Earths magnetic north, which if you think about it makes no sense, since magnets attract the opposite pole (North attracts South). What is really happening is the ‘north’ pole of a magnet has a negative charge due to the arrangments in the atoms and it’s attracted to the positive charge of the Earths magnetic north – so either the north end of our magnet is actually south or the Earths magnetic north is actually magnetic south.

How does electromagnetic induction work?

how electromagnetic induction works

Electromagnetic induction essentially is where a magnetic field or flux causes the flow of electrons in a conductive material. This is actually important to us in explaining what’s happening in our alternator, our north pole of the magnet is negatively charged, the south has a positive charge. This means that they will always try to attract an opposite charge, so when a magnet passes through or near an object with good electrical conductivity, the electrons in the conductor will be attracted to the south pole of our magnet, while the north pole  will repel the electrons. This creates a movement in the electrons, essentially creating a flow of current, some materials will have a better conductivity as the electrons are able to move more freely. You can see in my basic diagram above how the magnet will attract and repel the electrons (orange circles) in the wire thus creating the alternating flow of electrons or current – without getting too complicated alternating means the current flows in 2 different directions which produces a sine wave.

Now, what happens as our magnet passes through our coils is that the electrons are pushed and pulled creating our alternating current, so the current switches directions based up on whether the electrons in the coils are being attracted or repeled. This then means that at either end of our coil there is an intermittent electrical charge switching between positive and negative, so an LED attached to one end will only light up when the magnets push/ pull the electrons in one direction.

Whats the difference between alternating current (AC) and direct current (DC)?

We want to get all the power of the alternator and not just half of it so we need a way to create a constant flow of current/ charge/ electrons so that our LED will always light up no matter which way the magnets are moving. This is where our rectifier comes in, converting or AC to DC (Direct Current). Direct current is where the current flows in only one direction, classically this is described as going from positive to negative and in most electronics this is the model that is used, however, in physics it’s considered the other way around!

Now that’s all understood we can move on to building our rectifier for the generator

Shakeable Dynamo Part 4: Building the bridge rectifier


  • sir/mam
    i am not understanding the concept behind this emi.
    if u can make it more simpler so that it would be very easy for me and my friends to catch the logic behind this great concept.
    i am sorry if i had disturbed u in any means.

    • Hi Santhosh, which part of this do you not understand? To understand the basics behind what I’m talking about concerning atoms, protons, electrons etc… you’ll need to do a little bit of research about these for it to make more sense.

  • its good ,thanks for sharing with us

    • No problem – needs a bit of work though to make it useful 🙂

  • Sorry Larry – you are obviously a technical whiz but you physics are mixed up. Graphics are GREAT – but you are confusing charge and and magnetic poles. North is not a negative charge and south is not a positive charge. Charges are spinning like cars on a racetrack. If the positive charges move counterclockwise on the track (electrons moving clockwise) then north is up (skyward) and south is down groundward. A ferromagnetic material placed close by gets likewise excited and the electrons in their atoms follow suit to match the permanent magnet’s orientation. But polarization (what your figures are showing) is a different beast. The picture you drew would be what happens to atoms in the dielectric material of a capacitor or some solid-state storage devices. Unfortunately, induction is not as easily explained as that. I’m not sure I even really understand it. It just IS.

    • Hey Richard,

      Thanks for taking the time to comment, it’s great to get feedback like this as information is hard to come by or to understand most of the time and it’s why I write up all this stuff 🙂

      I did base my ideas on a few other sites concerning charge and polarisation difference at the poles which perhaps I should have quoted as maybe they also got it wrong, but more likely I did – I think I over simplified it somewhat by ignoring the electron movement in my initial diagram.

      Induction is basically magic and I think you’re right – it just IS 🙂 It only makes sense to me that it must work on an atomic level I can’t think how else it would work other than magnets carrying a charge in a certain way that repels electrons. If you have any decent info on the subject that you can point me towards that would be great.

      Cheers for taking the time though – I should update and correct this rather than potentially mislead people

  • Thanks – sorry if I sounded a little strong headed. I have had quite a few years of education in this area and was actually teaching a class at a technical school here which lead me to find your site. There are of course numerous textbooks, but I understand that you are looking for a nice summary. I will add a few comments because I simply can’t help myself. My suggestion is to look up the Lorentz force – you need to put on your 3-d thinking cap for that. Then, understand the idea of magnetic lines of flux. – well I was launching into a lecture – but I’ll stop there. keep up the good work. Thanks for accepting my comments.


    • Actually it’s really good to get feedback from someone who knows what they’re talkign about – it’s pretty hard finding decent information online about this sort of thing. For instance Lorentz force is something that I don’t know much about other than what I can find on Wikipedia and the like. Eventually I want to build up some decent sized wind turbines so understanding all of this is a must, please feel free to add more.

  • thanks so much, it helps a lot in my assignment.

  • Larry, i have heard that when you spin the rotor (and magnets) around in an alternator there is a force other then the friction of the bearings repelling the motion. there for when you pull more current from the wire the rotor would be harder to turn. this confuses me, as i was alway told its the spinning of the magnets within the wire coils that induces the current (maximum current is dependent on wire gauge and magnet strength)

    am i wrong?

    • Well simply it’s the magnetic force that’s repelling motion created by the coils, in quiet a few rotors the coils have an iron core which will magnetise thus attracting/ repelling the stator.

You must be logged in to post a comment.