Ohm’s law is the most basic and most useful electrical equation. It’s used frequently in car audio installation on both the power input and the power output side. Simply stated Ohm’s law is:
Where E is voltage measured in volts, I is current measured in amperes (amps) and R is resistance measured in ohms. Memorize this equation. You’ll use it A LOT in car audio. For example, if you need to figure out the current (amps) moving through a 12 volt circuit and you know the resistance of the circuit is 4 ohms, the equation would look like this:
E = 12volts
I = unknown
R = 4 ohms
I = E/R or I = 12/4 which is I = 3 amps
Another useful equation to know is the power equation:
P = E*I (power equals voltage multiplied by current or watts = volts * amps). From this we can substitute Ohm’s law for any values we don’t know. For instance if we need to know power but we only have amperage (I) and resistance (R) then we could substitute I*R in the power equation (because according to Ohm’s law E=I*R) and get P = I*R*I.