OHMS LAW

Why is ohms law so very important?

Ohms law, very obviously named after Mr. Ohm, defines the relationship between power, voltage, current and resistance. These are the very basic electrical units we work with. The principles apply to a.c., d.c. or r.f. (radio frequency).

What are the ohms law formulas?

To make it much easier for you I have put all the relevent formulas together for you here complete with worked examples of ohms law. You will notice the formulas share a common algebraic relationship with one another.

For the worked examples voltage is E and we have assigned a value of 12V, Current is I and is 2 amperes while resistance is R of 6 ohms. Note that "*" means multiply by, while "/" means divide by.

For voltage [E = I * R]       E (volts) = I (current) * R (resistance)   OR   12 volts = 2 amperes * 6 ohms

For current [I = E / R]       I (current) = E (volts) / R (resistance)   OR   2 amperes = 12 volts / 6 ohms

For resistance [R = E / I]   R (resistance) = E (volts) / I (current)   OR   6 ohms = 12 volts / 2 amperes

Notice how simple it is?

Now let's calculate power using the same examples.

For power        P = E² / R   OR   Power = 24 watts = 12² volts / 6 ohms

Also        P = I² * R   OR   Power = 24 watts = 2² amperes * 6 ohms

Also        P = E * I   OR   Power = 24 watts = 12 volts * 2 amperes

That's all you need for ohms law - remember just two formulas:

for voltage E = I * R and;

for power P = E² / R

You can always determine the other formulas with elementary algebra.

Ohms law is the very foundation stone of electronics!

Knowing two quantities in ohms law will always reveal the third value. I suggest you print these formulas out and paste them onto scrap cardboard to keep your ohms law as a handy reference until you are quite familiar with it.
 

Related topics on ohms law

electron theory

voltage

current

resistance

resistor colour code chart