Electromagnetism physics for idiots gas in dogs stomach


For electromagnetism all you need to know is what happens when you have + or – charges, what happens when they get close and what happens when they move. That’s it! For all of non-quantum EM there are only 5 formulas you need. The 4 Maxwell Equations and the Lorentz equation describe all of electricity, magnetism, light, sound, radiation, actually most of physics:

How bad can a topic be if you can describe it all with just 5 equations, you could probably fit them all on the back of a beermat. Now that you’ve seen the conclusion we can go to the beginning and read the whole story in detail. Unless you’re doing a university course you can get away with not knowing exactly what the equation mean or do, but this site will explain them later, first lets get back to basics. The Basics

Charge comes electricity merit badge pamphlet pdf in 2 types, positive and negative and is measured in Coulombs (C). If you have a charge on its own it emits a field in all directions. The field from a charge is represented by E as in E-lectricity. If you put another charge in the field it experiences a force. Like charges repel and unlike charges attract. The bigger the charge the stronger the force and the further away the charges the weaker the force, exactly what you’d expect. This relationship can be represented by Coulombs Law;

The ‘s are the two charges and is the distance between them squared. The other bit is just a constant which roughly equals 9000000000. (The exact derivation of this law can be found here). From these you can see that the force is just the field times by whatever charge you put in, . Using this you can work out the field or force between particles or atoms or anything with charge provided they’re not moving. Once you start a charge moving other things happen. Stuff Moving

which is known as the Lorentz force chapter 7 electricity and magnetism. The symbol does not signify multiplication, in this context it means Cross-Product. It’s basically a short way of writing “ times times the sine of the angle between”. This is because the field pushes at 90° to which ever direction its pointing AND which ever direction you are moving in. Now unless you’re doing EM past A-level you can forget all about the directions and angles and just write

Obviously is the force and is charge, and are the two fields previously described and is the velocity of the moving charge. The electric field is measured in the SI units of Newtons per coulomb ( ) or, equivalently, volts per meter ( ). The magnetic field has the SI units of Teslas (T), equivalent to Webers per square meter ( ) or volt seconds per square meter ( ) Circuits electricity jeopardy powerpoint

A circuits is basically just a series of moving charges with the occasional object or device in the way that affects the flow. Now when I say the electrons are moving around most people will think that their speeding around at close to the speed of light, but this is wrong. The actual electrons are moving EXTREMELY slowly, it’s the wave that travels fast. As stated above like charges repel, so put one electron next to another and they will move apart. With a current in a wire you basically have a tube of electrons and you’re adding one to one of the ends, this causes the next electron to move down which in turn pushed the next one and so on. So you have a Mexican wave like effect that moves quickly, but the electrons themselves are only moving slowly.

This says that the integral of the Electric field, , through a closed area is equal to the total charge inside of the area, divided by . is a constant called The Permittivity of Free Space and shows up all over physics along with which is The Permeability of Free Space. What this equation means is you can take ANY closed surface you like and find the field going through, provided you can do the maths. Usually you can’t. However there are a number of cases when its nice and easy. Cases when the field is coming straight out through the surface evenly. The cases are

These are the Gaussian surfaces. Basically with these surfaces all you’re trying to do is make life easier. You just make sure that the surface is always the same distance from the charge source and that the field is always going through at 90 degrees. You can then work out the gasbuddy nj integral with your eyes closed its that easy. The left hand side of Gauss’ law becomes E times the surface of the shape you chose.

Now in this something new has been introduced, . If you have an infinite line of charge then the total charge on it is infinite and there is no way of knowing how much of that infinite charge you would have inside your gaussian surface. That’s where comes in, its a value of charge per unit length, so if =4Cm and you have 5 metres then the charge is just 20C. That’s all is, just a value of charge.

Lets say you’ve got a charged ring and you need to know the field produced from it. Once again we’ll be employing one of the most important tools in physics, making stuff easier. Firstly we’ll only look at the field along the axis of the ring, otherwise things just get too complicated and it’s not worth the effort. Now lets just take a very small part of the ring and say that it’s a sphere. This isn’t really true, but the smaller we make the section the more we can make it resemble a point charge. So you have something like this

You want to find the field at a point along the axis gas prices map from the ring of total charge and radius . The little square section at the top, that’s the bit that you assume is a charged sphere. Now we don’t know how much charge is in that little section as you can make it any size you want so we just call the charge , a small amount of . So we now have

So there you have it, the field from a charged disk. All you need is the field from a point and some trig knowledge and you can work it out. I could have just given you the final solution, but this way you can see where it came from and then if you forget it you may be able to work it out from first principles like above. Gauss’ Law for Magnetism

Its like the ordinary gauss’ law in that it describes a field, this time its the magnetic field, . It says that the integral of B over a closed surface, is zero. Nothing. Every field line that goes out of the surface has an equivalent that goes in. There is no overall field. This means that its impossible to get sources of Magnetic field. Whereas electrons and protons are origins of field, from electricity vs magnetism venn diagram which field lines diverge from or converge to, there is no magnetic analogue. Magnetic field lines are always closed loops, no start, no end. This of course hasn’t stopped people from preparing in case we do find a magnetic monopole.

I’ll walk you through each bit to show you what it actually means. First we have the left hand side which is easy. Its just like Gauss’ law only the integral is over a different thing. Instead of finding the total field through a surface, , we are now finding the total field around a closed loop . That’s all that’s different with the left hand side, no more surfaces, just closed loops. Now on to the right hand side. First up we have a minus, noting complicated about that. Why its there will be explained later. Next we have another integral, and this one looks horrible. The symbol basically means a small wd gaster x reader change. So is a change in , and is a change in , where is time. The whole is the rate of change of , its how much is changing ( ) in a given time ( ). And that is being integrated over an area . is the area inside the closed loop , if you draw some random squiggly thing making sure that the line doesn’t cross itself and that it joins itself then the length around the line is your and the area inside the line is your . Simple yes? So the total around a loop is just equal to the minus of the changing through the loop.

Left hand side, easy, integral of B around a closed loop. Right hand side, not so easy. First lets ignore the bit, I’ll come back to that. Other than the , its very similar to Faradays law. You have another changing field integrated over an area, but this time its . This time though instead of multiplying by minus 1 you’re multiplying by . Once again these are two very important values in physics, alone and combined. They are at the very heart of EM. So your magnetic field around a loop is just equal to the changing E field going through it times by , but then you have to add on a bit. This is the bit. This is just the current going round the loop times by , this is because, as said in Stuff gas jockey Moving, if you have a moving charge i.e. a current, then you get a magnetic field. So you have to add the two bits together. There, done. Another Form of the Deep End