Georg Simon Ohm (1787-1854) was a German mathematician and physicist and a medalist of the Royal Society (a British scientific academy that was the scientific social clique of the time). He first conducted a systematic study of electrical resistance.

He came up with a thought that we now call Ohms Law (well yeah duh).

For most materials, resistance is constant over a wide range of applied voltages.

This law is often found to be expressed as:

How exactly does Ohm's Law explain this?

Well, he's the man-of-resistance so we first look at the equation that way:

if we graph that, R would be the slope of a straight line.

<pic Serway p541 17.5a>

But not all materials obey Ohm's Law!

So what happens? R changes (oh no!) and the graph would look a little more like this:

<pic Serway p541 17.5b>