How To Apply Ohm’s Law

Electricity operates within predictable boundaries. We have come to identify these boundaries as Ohm’s Law. Ohm’s Law was developed as a means of explaining how electricity operates within a closed circuit. The Ohm’s Law formula helps to communicate the relationship between different properties within an electrical circuit. We can use Ohm’s Law to explain what has occurred, as well as what will occur, when certain conditions are imposed upon an electrical circuit.

The basic properties of the electrical circuit are: Voltage, Current, and Resistance. These are specific, defined, and do not change – assuming all properties remain constant. However, change the value of just one of these properties, and all properties will adjust value accordingly.

Ohm’s Law is the most basic of electrical formulas and was developed by simply observing the properties of electricity within the electrical circuit. Electricity does not behave as it does because of limitations imposed by Ohm’s Law formula; the formula simply represents our observations of behavior already occurring within the electrical circuit.

While Ohm’s Law is but an introductory rung on the ladder of electrical science, a basic understanding of an electrical circuit is necessary in understanding how Ohm’s Law, as a formula, is applied to a simple circuit.  A simple circuit consists of a power source, a load, conductors, an overcurrent device and a control device. Current will flow in this simple circuit if there is enough voltage present to overcome any circuit resistance.
Voltage is considered pressure within an electrical circuit; it is appropriately called, Electromotive Force. This pressure or “force” is caused by dissimilar electrical poles wanting to balance themselves. The push and pull imposed upon electrons in a conductor connected to these dissimilar poles, will force the electrons to move if there is a complete path for them to travel on. The only thing that can stop the electrons from moving is resistance applied beyond that of the voltage pressing them to move, or a break in the circuit that disrupts the flow of those electrons. It takes one volt (V) of this Electromotive Force to push one amp (A) of current through one ohm (Ω) of resistance- this is Ohm’s Law. Voltage(E or V) is equal to Current (I) multiplied by Resistance (R). Or in other words, E(or V)=IR.


  • Volts(E or V) = Electromotive Force, again this is the pressure that forces electrons to move along the conductor (and through a load) in a complete circuit.
  • Current(I) = Intensity, represents current flow in the circuit. Remember, the “intensity” of a circuit’s current flow is measured in Amps.
  • Resistance(R) = Ohms, is resistance to current flow. Resistance can be intentional or by accident, but either way it is the opposition to free-flowing current within the circuit and is represented as Ohms on your electrical meter. Zero Ohms or close to it, means literally no resistance to current flow. Copper has a very low Ohm reading per foot and is a premium material for constructing effective conductors.

Let’s look at Ohm’s Law symbols within the Ohm’s Law Triangle.

Remember, Volts(E or V) equals Current(I) Multiplied by Resistance(R)

It is not an uncommon practice to use the Ohm’s Law Triangle as a visual aid when remembering the three equations of Ohm’s Law.

To find the missing value in a real-world Ohm’s Law equation, just cover the letter representing the missing value in the triangle and use the remaining two values to calculate for that missing value.

For example: If you know a 120 Volt(E or V) lamp measures .625 amps(I) of current flow when in use, how many Ohms of resistance is being offered by the lamp?

120 Volts(E) divided by .625 amps(I) equals 192 Ohms(R) of resistance.

What if you know the measurable amps(I) of current flow and the resistance(R) of the lamp filament? Can you then calculate the voltage being applied to this lamp? Look at the Ohm’s Law Triangle below to determine your answer.

The Current(I) multiplied by the Resistance(R) equals the Voltage being applied to the lamp.

Ohm’s Law Triangle Rule
Remember, when looking at the Ohm’s Law Triangle, if the numbers are side by side, you multiply, if the numbers are one on top of the other, you divide.

Ohm’s Law and many other electrical formulas provide us the means by which we can understand the most basic of principles of electricity and current flow. These many formulas allow us the opportunity to see into the past as well as into future electrical applications. One might say these formulas give us a leash of sorts, if not to control this phenomenon, then perhaps to at least hang on!

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