1. Introduction: A Line That Tells You the Resistance
You already know one short sentence about electricity: push harder and more current flows. The "push" is the voltage V across a wire. The "flow" is the current I through it. Earlier you met resistance R — the one number for how hard a wire fights that flow.
Now we do something a real scientist does. Instead of just talking, we take readings. We change the push, we measure the flow, and we plot the two against each other on a graph. That single picture — a V-I graph — will let you see the resistance with your eyes, not just calculate it.
Here is the idea. For many conductors, when you draw V against I you get a perfectly straight line passing through the corner of the graph. That straight line is the signature of an ohmic conductor — a conductor that obeys Ohm's law. And the steepness of that line is the resistance.
By the end of this lesson you will be able to draw this graph correctly, read the resistance straight off it, and tell at a glance whether a conductor is ohmic or not.