## What is electricity?

What is the difference between electric current and electricity?

Good questions. The term “electricity” is very old. In modern times we have learned so much about how electricity works in detail (charge, electrons, voltage, current, etc.) that the word “electricity” is now used only as a vague name for the whole field.

A “current” is the movement of something that flows, (usually a liquid like water or lava). When we get electrons to move through a wire we call it an “electric current” and measure it in Amperes. An electric current is the “flow of charge”. You might hear someone say “An electric current is the flow of electricity,” but that is kind of old-fashioned sounding and not very precise.

Force or energy? When you place two electric charges near each other they experience an “electric force”. You know the rule: Like charges repel, unlike charges attract. That is the main force in electricity.

If you have two like charges (say two electrons) and you push them closer together it takes effort on your part. You have to put some energy into the electrons to make them move closer (the energy you apply has to overcome the force of repulsion). That energy, when defined precisely, is what we call “voltage”. Two electrons pushed close together have higher voltage than if they were farther apart.

# Does resistance make current go down?

Well. I’m a bit confused. Basically, the resistor reduces current flow. But it appears to be reducing voltage instead.

Ohm’s Law is an equation with three variables, V = I R. In almost all cases the value of R is not really a variable, it is a fixed value corresponding to the physical properties of the resistor object.

That leaves V and I as the real moment-to-moment changing variables. If you arrange Ohm’s Law like this,

R = V/I

you see R is the ratio of V to I. R does not specifically make I or V go up/down, instead, it sets the ratio between the two variables.

If R changes, then either V or I will change to restore the ratio and keep Ohm’s Law true.

So you can say a few true things… If R increases AND V is held constant, then I decreases. If R increases AND I is held constant, then V increases.

If you are holding a single resistor in your hand the only thing it “knows” how to do is maintain a fixed ratio of V to I. It can’t set either V or I separately, but it can determine the ratio.

When you put the resistor in a circuit, the other things it is connected to help determine which of V or I adjusts to make Ohm’s Law true. For example, if you connect R to a battery, the battery produces a fixed voltage V, like 1.5V. So you know the resistor will allow enough current to flow to make the ratio right, R = 1.5V / I, or I = 1.5V/R.

The battery “cares” only about its voltage; it will provide whatever current the resistor “asks for”. The resistor only “cares” about its V/I ratio. Together they determine the current.