 When I say electricity, we tend to think about the stuff that powers computers or lights or heaters and when I say magnetism We tend to think about compass needles or maybe the things that stick to fridges or possibly the elements of motors But relatively recently in human history, we discovered that these two things electricity and magnetism We're actually part of one thing called electromagnetism and this theory Defines nearly every interaction we ever experience Electromagnetic forces are why I don't fall through this floor They describe all of chemistry and interaction between all materials Electric fields are what make up light x-rays gamma rays Wi-Fi infrared television radios signals Electromagnetic theory warned us about relativity It's how we first discovered the existence of relativity and it also led to the discovery of quantum field theory Which is our deepest theory of stuff light matter everything Every touch taste smell and sight that you ever experience is coming to you courtesy of electromagnetism But of course, that's a very modern Realization it took a very long time indeed for us to understand that all these different aspects of nature We're in fact coming from the same fundamental principle in a sense That's the real power of physics It lets us take what look like a whole lot of different phenomena and combine them using one simple theory So for example with gravity we discovered that the way things fell on earth We're also explained exactly how the stars and planets wheeled in the sky in nature You see electrical phenomena that are very clear in things like lightning or electric eels But the first recorded experiment that dealt with the discovery electricity was in fact in around 600 BC Where a Greek mathematician noted that if you rub amber and fur together then you can create a spark And you can also store on the amber what looks like some kind of property that would cause things like hair to suddenly repel itself This is what we call static electricity these days And this was the first discovery of how you could put a charge on an object and this property that the amber got that We now call charge we now understand is a fundamental property that things can have in the universe just like mass So charge is measured in coulombs Which is denoted by a capital C. It can be positive or negative That's different to mass which can only be positive and it's also conserved So you can't create or destroy a net charge So what's happening when you rub amber and fur together? You're actually moving some of the particles from one to the other And so one of them is becoming on average more positively charged and the other ones becoming more negatively charged So the total amount of charge hasn't changed But each item now has a non-zero net charge and the reason we know that charges exist is that when things have charge Then they interact with each other And the theory of how charges interact is precisely the theory of electromagnetism And there's two ways of thinking about electromagnetism, which are almost equivalent The first is that charges attract and repel in other words if I have two positive charges They'll each experience a force due to the other one and that will cause them to repel Same if they're both negative charges and you might already know that if I have a positive charge and negative charge Then they'll experience a force that is attractive and the second model is that charges make an electromagnetic field and Then electromagnetic fields cause charges to feel forces So you can basically see that these two models are equivalent in both cases You have a force on one charge due to another charge Except in this second model you've got a charge making a field and in the field making a force And so you've got this extra step and so a perfectly reasonable question would be well Why add this extra step? Why have a model that has this extra complication in the existence of these fields in it? And the answer is that in the long run Using these fields actually makes things simpler to describe It turns out that if you don't have those fields then you don't have such things as conservation momentum and energy Because these fields themselves this actual field carries momentum and energy When you have something like light or x-rays or Wi-Fi or something that radiation is just this wiggling electromagnetic field And that carries energy from one place to another and so if we include that then all the rest of our physics and the rest of our understanding is much easier to handle