Professor Dave here, I want to tell you about magnets. We have known about the magnetic properties of certain types of matter for thousands of years, and have long utilized this phenomenon for navigation in the form of a compass, and also to display good report cards on the fridge. A few different kinds of magnets are instantly recognizable, like the popular horseshoe variety, and most people are aware that these attract iron-containing objects. Any bar magnet will have ends called poles. One will be the north pole and one will be the south pole, which were named as such because of the way a suspended bar magnet will orient with respect to the cardinal directions. This is how a compass works, it's just a magnetic needle that always points north. Like poles repel and opposite poles attract, just like electric charges. The difference is that opposite charges can be isolated, whereas no matter how many times you cut a magnet in half it will always contain both poles. To fully understand the properties of matter that allow for magnetic behavior, we must understand the electron configurations of the atoms in the magnet, and we must therefore learn some chemistry. If you are interested you can check out my general chemistry series for more atomic knowledge than you can shake a stick at, but for our purposes here it will suffice to understand that most materials contain atoms with all of their electrons paired up in orbitals with one spin up and one spin down such that they cancel each other out, but some substances like iron, cobalt, and nickel have electrons that aren't cancelled out, and some of these can be called ferromagnetic. In these materials the atoms will adopt an orientation such that all of their net spins are aligned in parallel fashion and this phenomenon which we can refer to as a magnetic domain will generate a magnetic field. A magnetic field can be depicted using field lines just like an electric field, and though they will appear to begin at the north pole of the magnet and end at the south pole, they have no true ends. They are closed loops that continue through the magnet itself. In this way earth itself is a giant bar magnet with the magnetic north pole about 1,500 kilometers from the geographic North Pole, and the magnetic south pole about the same distance from the geographic South Pole. The geographic poles mark Earth's axis of rotation but the magnetic poles exist because of the way atoms are distributed in Earth's iron core, which align their spins just like the atoms in a bar magnet. The magnetic poles actually change their position slightly over thousands of years as material in the core changes position. There is so much magnetized material in the Earth's core that the magnetic field generated is absolutely immense, stretching far out into space. This field interacts with high-energy charged particles that race towards us from the Sun and deflects them towards the magnetic poles to produce the aurora borealis when these particles collide with molecules in our atmosphere. These become excited and release colorful light upon relaxing back to the ground state. Without the Earth's magnetic field we would be at tremendous risk from this kind of radiation and life on Earth probably wouldn't be possible. Electric current is able to deflect a compass needle, and magnetic fields affect the paths of particles with electric charge, so it wasn't long until we realized that electricity and magnetism were two sides of the same coin, which was then dubbed the electromagnetic force. We now realize this is true because it is the motion and orientation of electrons that produce magnetic fields. We can use the right-hand rule to show that if you grasp a current carrying wire in your right hand with your thumb pointing in the direction of the current, your other fingers will wrap in the direction of the magnetic field that is generated by the current. We later came to understand how electric and magnetic fields fluctuate together to generate electromagnetic waves. This was the first time two seemingly separate forces were unified, but it wasn't the last. We have been able to unify most of the fundamental forces through our study of modern physics, and one of the primary objectives of physics today is unifying all of them into one grand unified field theory, a so-called theory of everything. Everything we have discussed in this classical physics course was discovered between the 17th and 19th centuries, and at the turn of the 20th century, things got a lot weirder thanks to Einstein and some of his pals. We learned that things can be both particles and waves, that time flows at different rates for different observers, and that space itself is curved around massive objects. So if you feel like you've sufficiently mastered the concepts presented in this series, I'll see you in the modern physics course. Thanks for watching, guys. Subscribe to my channel for more tutorials, support me on patreon so I can keep making content, and as always feel free to email me: