Physics
Course Description
1. (General Physics) the branch of science concerned with the properties of matter and energy and the relationships between them. It is based on mathematics and traditionally includes mechanics, optics, electricity and magnetism, acoustics, and heat. Modern physics, based on quantum theory, includes atomic, nuclear, particle,and solid-state studies. It can also embrace applied fields such as geophysics and meteorology.
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Current
So what is electric current? Electric current is the rate of charge flow. So electric current is something that happens when I have charge moving through a conductor or whatever.
Whenever I've got charge moving, I've got an electric current. So current is equal to charge passing by a given point divided by how long it too that charge to pass by that given point. It's given by the symbol i and the unit, of course SI units, what's charge? Coulombs. What's time? Seconds. So we got coulomb per second. One coulomb per second is called one ampere or amp, alright. So the current gives the number of coulombs of charge passing a given point in one second. So if for example my current is 3 amps, then that means that every second, 3 coulombs of charge pass by my given point. Alright.
There's the convention that essentially everybody uses for current. And that is that current is taken to be in the direction of positive charge flow. Now we use this convention despite the fact that in almost every situation, electrons are usually going the other way. But it's kind of easier for us to talk about positive quantities and you know what, Ben Franklin was good but he didn't know everything. So he assigned the electron negative charge instead of positive. Oh well, you deal with what you're given.
Alright. So potential difference is what causes current to flow. If I've got a high potential over here and a low potential over here, then my current is going to go this way because positive charge wants to go away from the high potential and towards the low potential. So that's the way that we can make current flow, is we can make one side of a conductor at a high potential and the other side at a low potential. So we always flow from high to low.
Whenever I've got charge moving, I've got an electric current. So current is equal to charge passing by a given point divided by how long it too that charge to pass by that given point. It's given by the symbol i and the unit, of course SI units, what's charge? Coulombs. What's time? Seconds. So we got coulomb per second. One coulomb per second is called one ampere or amp, alright. So the current gives the number of coulombs of charge passing a given point in one second. So if for example my current is 3 amps, then that means that every second, 3 coulombs of charge pass by my given point. Alright.
There's the convention that essentially everybody uses for current. And that is that current is taken to be in the direction of positive charge flow. Now we use this convention despite the fact that in almost every situation, electrons are usually going the other way. But it's kind of easier for us to talk about positive quantities and you know what, Ben Franklin was good but he didn't know everything. So he assigned the electron negative charge instead of positive. Oh well, you deal with what you're given.
Alright. So potential difference is what causes current to flow. If I've got a high potential over here and a low potential over here, then my current is going to go this way because positive charge wants to go away from the high potential and towards the low potential. So that's the way that we can make current flow, is we can make one side of a conductor at a high potential and the other side at a low potential. So we always flow from high to low.