Even though most of us have a natural, built in aversion to math, there is one formula dealing with electrical systems that we absolutely have to know about. This law was formulated by Georg Ohm back in the 1860’s and believe it or not, it is still in effect.
The best way to make use of Ohm’s law is to know it, and understand it and then use it instinctively, rather than having to think about it. Many times when analyzing an electrical circuit, it is helpful to consider Ohm’s law and how it affects circuit operation.
Ohm’s law is the single statement that draws together all the information we have studied thus far. It is deceptively simple and yet amazingly inclusive. Remember we have discussed Voltage, Current, Resistance, and Circuits. The formula for Ohm’s law comes in several forms, but we will start with:
I=E/R
Where I is current, E is voltage, and R is resistance. This formula states that in order to determine the current in a given circuit, you divide the circuit voltage by the circuit resistance.
As a quick example, if the voltage of a circuit is 12vdc, and the resistance is 2 ohms, the current would be:
I=12/2=6 amps.
If you have been following this series, you will remember one of my rules for working on electrical systems, and that is to have an idea of what to expect when you make an electrical measurement before you make it. Using Ohm’s law as described above enables you to look at a particular circuit and realize that you expect to measure 6 amps flowing in the circuit.
There are several other variations to this formula and we will talk more about them next time.