Understanding Magnetism – Generating Magnetic Field

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For us to know more about the electric motor, we need to know about magnetism. So let me create a permanent magnet in my left hand. So this is a permanent magnet. And you realize that it comes with a North pole and South pole. It doesn’t come with only one pole, which is a “monopole”. Right now nobody has discovered a magnetic monopole before. So it always comes with a North pole and South pole. And you realize there are some lines that are running from the North pole, and returning back to the South pole. Those are called magnetic flux/field lines. They are the ones that are responsible for the attraction that you feel when you put a magnet next to some iron filings or paper clips. Besides using a permanent magnet, to create magnetic field, you can also use copper wires. And I think you know what I’m talking about, you can use an electromagnet. So if use a copper wire, by itself, if you only have a copper wire, when you pump a current through a copper wire, or any conductive material, there will be a magnetic field that will be created revolving around the copper wire. Like this. So you can actually create a magnetic field that is similar to the magnetic field just now, by using this copper wire and coiling it out in a helical manner. Like so. And when you pump a current through it, you realize that you will generate a magnetic field similar to the permanent magnet that you saw just now. So the convention is that you use the “right hand rule”: So you use your hand and your fingers is pointing towards the direction of current flow, and your thumb is pointing towards the North pole or where the magnetic flux is coming out from, and it will come out from your thumb and return back from the bottom. So it is quite wonderful, you don’t need a permanent magnet that is dug out of the ground; you can actually create your own magnet using copper wires that you coil up and pumping current though. So there is actually an advantage and a disadvantage of using copper wires against permanent magnet. What is the advantage and disadvantage of using an electromagnet or copper wires vs a permanent magnet. So it’s great to see all your responses, let me tell you one disadvantage of using the copper wires. So when you pump current through the copper wires, what happen is that it will heat up. And if you pump more current, it will heat up more. It come to a point where you pump a current too high, and the temperature is about perhaps 140 degrees celcius where the copper will start to oxidize and when it oxidize you can think of it as being “burnt”. And it’s unable to conduct electricity well anymore. So there is a limit to the amount of current that you can pump into the copper wire. So if you want more magnetic flux, you will need a lot copper wire and you will need more current. And that is the second problem right, you have to use power, you have to waste power in order to generate magnetic field using copper wires. And this power is lost in many ways, we call it “Copper Loss” and Iron Loss”, but you’ll learn that later. But there is also one very big advantage of using copper wires or electromagnets compared to a permanent magnet is that if you pump one amp, you will get a certain amount of magnetic field and if you pump two amps, you will get double that amount of magnetic field. The amount of magnetic field is proportional to the amount of current that you pump through the copper wires. This is exciting because now you can control the shape and the amount of magnetic field that is created. Those are the two disadvantage and advantage of using an electromagnet as compared to using a permanent magnet.

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