About this video
Magnetic force is part of the fundamental electromagnetic force. Magnets always have a north and a south pole that can never be separated; unlike poles attract and like poles repel, and the force acts without contact through a magnetic field whose lines always loop. Stronger magnets and closer distances give stronger forces, and a current-carrying coil becomes an electromagnet whose strength depends on the current.
You'll be able to
- explain that north and south poles always come together and cannot be separated.
- predict whether two magnetic poles attract or repel.
- describe how magnet strength and distance affect magnetic force.
- explain how an electromagnet works and why it is useful.
Key words
- magnetic pole
- One of the two ends of a magnet, north or south, where its effect is strongest.
- magnetic field
- The field around a magnet that can put forces on other magnets; its lines always loop from north to south.
- non-contact force
- A force that acts without the objects touching.
- permanent magnet
- A magnet whose magnetism is always on and whose properties are pretty much fixed.
- electromagnet
- A coil of wire that becomes a magnet when an electric current flows through it.
- electromagnetic force
- The fundamental force that combines electric and magnetic forces.
Transcript
- [Narrator] Gravity is a fundamental force. But most of the other forces that we deal in our everyday life, like tension, friction, normal forces, et cetera, they're part of a fundamental interaction. A fundamental force called the electromagnetic forces. And from the name itself, we can see there are two parts to it.
We have the electric part and the magnetic part. We combine them together as a single force today, but we're gonna study them separately. In this video, let's talk about the magnetic force. Now, you played with magnets. So you probably know that magnets can put magnetic forces, right?
And you might know that magnets have two poles. You have the north pole and the south pole. This is very similar to how you can have a positive charge and a negative charge, but there is a big difference, you know, the big difference is positive and negative charges can be separated.
But can you separate a north and a south pole? Well, at first it seems like, yeah, just cut a magnet. You get a north and south pole, right? No, you don't. If you cut a magnet, you know what you'll get? You'll actually get two tiny magnets each having its own north and south poles.
And if you try to create again, well again, you'll get tiny magnets each having north and south poles. You can never, ever separate the south and the north pole of a magnet, they always come together. Okay, that's pretty interesting, right? But let's talk about some other features of magnetic forces.
While playing with magnets, you may have noticed that you don't need them to be in contact to exert a magnetic force, which means magnetic forces are non-contact forces. And again, that brings up the question, how do these forces work? Well, just like in the case of gravity and electricity, they work via fields.
So in our model, the bar magnet, for example will produce a magnetic field, okay? You can actually see these magnetic fields. If you pour tiny iron filings, they will orient themselves along the field lines. And you can actually visualize the field. You can see the field lines curve.
That's beautiful, isn't it? So we can now draw these field lines, and this is kind of what it'll look like. The field lines usually, I mean, our convention is they start from the north and they end into the south. But they don't just end there inside the magnet, they actually loop back.
I mean, this drawing is not all that great, okay? But the whole idea is these lines will loop back. Again, this is very different than what we find in electric fields or gravitational fields for that matter. They don't loop over there. Here, they loop. Magnetic field lines will always loop.
Even these ones will go and loop back. They will always loop. And if you have another magnet close by, then that magnetic field can put a force on that magnet and they can turn it. And that's how if you put a lot of compasses, which are tiny magnets, they can turn according to the direction of the magnetic field.
Okay, so from this, can we think about the direction of the magnetic force? Yes. Again, you probably know that unlike poles attract each other, if you bring a north pole close to the south pole, it'll attract it. On the other hand, if you bring like poles close together, they'll repel.
Unlike poles attract like poles repel each other. So that's about the direction of the magnetic force. But what about the strength of the magnetic force? Well, if you have strong magnets, they'll have stronger magnetic fields, and they will have stronger magnetic forces, right?
So stronger magnets, well will exert more force. But what else decides this, you know, how strong the force is going to be? The magnetic force is going to be? Well, distance. If you have two magnets very close to each other like we have over here, north and south pole almost, you know, is touching each other, the magnetic force will be very strong.
In fact, sometimes it'll be hard to even pick it apart. You may have noticed this. But what happens if you bring them farther apart? The magnetic force will get weaker with distance. So if you, you know, separate them and bring them farther apart, now you can hardly feel the attraction because the magnetic force gets weaker with distance.
And you can see that again with like poles as well like poles repel each other. You can see that a lot when they're close. But when you bring them farther apart, well you can hardly feel that force at all. So, magnetic forces get weaker with distance. This is very similar to what we find in electricity or for that matter in gravity.
Now here's the last question. These are all permanent magnets. They produce magnetic fields and they exert magnetic forces. What about materials that are not permanent magnets? Can they produce magnetic fields and exert magnetic forces? Looks like snow, right?
But they can by passing an electricity. For example, copper wires, well, they're not magnetic, they're not permanent magnets at all. However, if you pass a current through them and you coil them up like this, they will act like a magnet. They will generate a magnetic field.
We call such magnets electromagnets, because they're magnetic due to electricity, which is pretty cool. This is very different from, you know, permanent magnets, they're not permanent magnets, they're in fact temporary magnets. They're magnetic as long as electricity passes through them.
And you can look at their magnetic field. And it's very similar to what you get in a bar magnet, right? Very similar to that. One side acts like a north pole, another side acts like a south pole. So these are temporary magnets. And the beautiful thing about them is you can, you know, alter their magnetic properties.
You can turn off the electricity boom and then, you know, the magnetic fields turn off, they don't behave like magnets anymore. You turn on the electricity, they behave like magnets. And guess what? Their magnetic fields depend on how strong the current is. So if you put a stronger current, you get a stronger magnetic field, you get a stronger electromagnet.
That's what makes electromagnets so awesome. You can change their properties, unlike permanent magnets, whose properties are pretty much fixed, right? So this also means that if you get a giant coil and you can put a lot of current through it, oh, you can create some very strong magnets.
That's basically how your junkyard magnets, for example, work. They're so strong that, you know, there's a current, they're electromagnets. We use currents, strong currents generate very strong magnetic fields, so strong that they can lift stuff up. You should never be anywhere close to such magnets can be very dangerous if you're wearing something that is magnetic, you know?
And another example of that is in your MRI scans, MRI machines require very strong magnetic fields and we generate them via not permanent magnets. Nope. We use electromagnets giant coils with electricity running through them. So, long story short, magnetic force is a part of the fundamental electromagnetic interaction.
It's a non-contact force. And what about its direction will unlike poles attract and like poles repel? And what about its strength? Well, stronger permanent magnets will exert more force. But on the other hand, when it comes to electromagnets, more currents, if you have more currents, then they can exert more force.
And on the other hand, when it comes to distances, well the magnetic force gets weaker with distance.
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