I am taking AP Physics right now (I'm a high school student) and we are learning about circuits, current, resistance, voltage, Ohm's Law, etc. I am looking for exact definitions of what current, voltage, and resistance are.
My teacher, as I'm sure most physics teachers do, compared a wire with current flowing through it to a pipe with water flowing through it. The thinner the pipe, the more 'resistance'. The more water pressure, the more 'voltage'. And the faster the water travels, the higher the 'current'.
I took these somewhat literally, and assumed that current is literally the velocity of electrons, voltage is the pressure, etc. My physics teacher said that the analogy to the water pipe is only really used for illustrative purposes. I'm trying to figure out exactly what current, resistance, and voltage are, because I can't really work with a vague analogy that kind of applies and kind of doesn't.
I did some research, and found this page which provided a decent explanation, but I was slightly lost in the explanation given.
Let me know if this question has already been asked (again, remember: I don't want an analogy, I want a concrete definition).
Edit 1: Note, when I say 'exact definition' I simply mean a definition that does not require an analogy. To me, an exact definition for a term applies to every use case. Whether I am talking about a series circuit, a parallel circuit, or electric current within a cell, the 'exact definition' should apply to all of them and make sense.
Best Answer
Before explaining current, we need to know what charge is, since current is the rate of flow of charge.
Charge is measured in coulombs. Each coulomb IS a large group of electrons: roughly 6.24 ˟ 10^18 of them.
The “rate of flow” of charge is simply charge/time and this calculation for a circuit gives you the number of coulombs that went past a point in a second. This is just what current is.
Resistance is a circuit’s resistance to current; it is, like you said, measured in ohms, but it is caused by the vibrations of atoms in a circuit's wire and components, which results in collisions with electrons, making charge passage difficult. This increases with an increase in temperature of the circuit, as the atoms of the circuit have more kinetic energy to vibrate with.
Voltage is the energy in joules per coulomb of electrons. This is shown though the equation E=QV where the ratio of Energy over charge= voltage. This is granted by the battery, which pushes coulombs of electrons, with what we call electromotive force. However when it is said that the potential difference across a component is X volts, it means that each coulomb is giving X joules of energy to that component.
Note: if an equation doesn’t make intuitive sense to you, chances are it is a complicated derivation, and to understand it you’ll have to learn its derivation.