Principles of Electricity

Ohm's Law

Thus far, we have discussed current, resistance, and voltage. Now we shall discuss the important relationship that exists between the three. Around 1840, German physicist Georg Ohm noted that there was a distinct mathematical relationship between Voltage, current and resistance. He then wrote the basis for what we now call OHMS LAW . Ohm's Law states that Voltage (in Volts) is equal to the product of the current flowing through a resistance within a circuit. In other words... Voltage = Current times Resistance.

Now comes the bone in the throat of the student. While we measure Voltage in Volts, we often use the letter E to represent Voltage. This is because another word for Voltage is ELECTROMOTIVE FORCE, which is shortened to EMF or simply E. Also, we use the letter I to represent current. So that our formula becomes:

So what does this mean? Simply put, if we have a resistance of 10 Ohms (R=10), and a current of 10 Amps(I=10), we will have a Voltage of 100 Volts, because 10*10=100 (E=100).

Ohms law can also be stated two other ways. By using basic algebra, we can turn the formula around to make it say:


Learning about Ohm's Law is fine and dandy, but if you are going to USE Ohm's law on a regular basis, you really ought to memorize it. Memorizing Ohm's law may sound like a time consuming and daunting task, but if you do it the Electronics Theory.Com way - you'll have it committed to memory for life within a few minutes!

You just have to imprint a picture in your mind. Years ago, Native American Indians used to roam the plains of the United States. These Indians would look across the plains, and see all kinds of animals. They would see rabbits running across the field, and eagles soaring in the sky. Now, picture things from the Indian's stand point - he sees the Eagle flying over the Rabbit:

Say to yourself Indian equals Eagle over Rabbit.

Now just use the first letter of each word: I = E over R, which is this formula:

However, from the Rabbit's point of view, he sees things a little differently. The Rabbit looks out and sees the Eagle flying over the Indian.

Say to yourself Rabbit equals Eagle over Indian.
Now just use the first letter of each word: R = E over I, which is this formula:

Finally, the Eagle up in the sky sees both the Indian and the Rabbit standing on the ground together.

Say to yourself Eagle equals Indian and Rabbit together.
Now just use the first letter of each word: E = IR, which is this formula:

Now if you simply remember the story of the Indian, Eagle and Rabbit, you will have memorized all three formulae.
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