 We can use compasses to investigate magnetic fields. A compass needle gives us the direction of the magnetic field at a point. The needle acts almost like a vector in vector fields. It points tangential to the field line at its position. The compass needle demonstrates direction exactly like a vector would, except it doesn't have magnitude. Sadly, compass needles don't shrink or grow based on the strength of the magnetic field it's in. We know what the magnetic field around a magnet looks like from previous experiments, but magnetic fields are a type of vector field. And ion filings don't show the direction of the magnetic field, so we'll use a compass to find the direction of the magnetic field around a magnet. To draw the magnetic field around a magnet, we need to know the direction that the magnetic field points in. We can use a compass to identify the direction at different points. Remember that the red arrow of a compass points north. So at a point directly below the magnet, the compass points up. And directly on top of the magnet, the compass also points up. Slightly to the side, you can see the compass starts changing directions. Now if we do this for lots of points around the magnet, we'll get the magnetic field. So if we connect these vectors, we'll get the field line representation of the magnetic field around this magnet. The field lines around a magnet found with a compass has the exact same shape as the field lines indicated by ion filings. With this picture though, we also get the direction of the magnetic field. The magnetic field lines always come out from the north pole of the magnet and point towards the south pole of the magnet. If you think back to how we analyzed the electric field around charged particles by looking at how a positive particle will behave, this is similar. In this case, we pretend that there is a north pole of a magnet in isolation and see how that pole behaves. Monopole means single isolated magnetic pole. So if there was a north pole by itself, it would be a monopole. Mono for one. Dipole means pair of equal and oppositely charged poles. So that's a magnet with both a north and south pole. The magnetic field around a bar magnet looks very similar to the electric field around two oppositely charged particles. The positive charge and the north pole of the magnet behave similarly. Same for the negative charge and south pole. The main difference is that charge can exist independently of each other. So it is possible to have a single positive charge or single negative charge without the other, while magnets are dipoles. Theoretically, monopole magnets could exist, but we haven't found any yet. The magnetic field around multiple interacting magnets is more complicated. We could do the same thing and use a compass to draw out the vector field and then draw in the field lines to find the magnetic field. But that's rather tedious. So instead, I'll just show you what the magnetic field around two magnets look like. In image one, the magnets are placed end to end with the north poles facing each other. The field lines come out from the north pole and go to the south. In image two, the magnets are still placed end to end, except this time the north and south pole are facing each other. One of the field lines coming out from the north pole of the left magnet goes into the south pole of the right magnet. However, one of the other lines comes out of the north pole of the left magnet and goes into the south pole of the left magnet. So it doesn't matter if the field line goes into the left magnet south pole or the right magnet south pole. In image three, we have two magnets parallel to each other, with the top magnet south pole being closer to the bottom magnet's north pole and vice versa. And again, the field lines come out of the north pole and go into the south pole. And just like in image two, it doesn't matter which magnet the field line comes out of or goes into. It is possible for the field line to go to a different magnet than the magnet it came from. And here we have two parallel magnets except with the south poles and north poles facing each other. And again, the field lines come out from the north pole and go into the south pole. Looking at these images, we know from real life experience that the magnets in image one and four would repel each other. And the magnets in image two and three would attract each other. The field lines in image one and four go back to the magnet from where it came from. While in image two and three, the field lines can come from a different magnet than the one it goes to. Magnets have many real life applications, aside from being really fun to play with. They are used to seal fridge doors, store data in computers, using every motor and so much more.