ABSTRACT
The current passing through the carbon is proportional to the voltage difference
between its ends.
This was first discovered, using lengths of wire, by Gregor Ohm, so it is called Ohm's Law. It applies to all conductors. We can state it as an equation:
You may have noticed in your class that different people, working with different pieces of carbon have found different constants. The value of the constant is a property of a particular piece of carbon. We call it the resistance of the piece of carbon. Now we can write the equation like this:
If we are given any two of the quantities, we can calculate the third. These three equations are used more than any in electronics, so you will need to remember them. An easy way of remembering is to memorize this diagram:
To use the diagram, cover the quantity that you want to calculate. The diagram shows the remaining quantities as they appear in the equation.
