Ohm’s law: definition and more

Electrical engineering is incomplete without ohm’s law. It is the most basic building block of electrical engineering. So, you must understand ohms law in detail.

Ohms law represents the relation between voltage, current, and resistance. A german physicist Georg ohm explained it in 1827. “ohms law” is named after the German physicist.

Ohm’s law statement

Ohms law states that the voltage applied between two points is directly proportional to the current flowing through it keeping all physical conditions constant. It is measured in ohms.


V = IR

In the above expression voltage ‘V’ is equal to current ‘I’ multiplied with resistance ‘R’.


V = voltage across the conductor (in volts)

I = current through the conductor (in amperes)

R = resistance of the conductor (in ohms)

Now, you can also obtain the values of the other two variables ( current and resistance ) of ohm’s law from the above equation.

I = V/R                           R = V/I

Important point: It is only valid if the physical conditions like temperature remain constant.

Read More: 2 Basic kirchhoff’s circuit law

Triangle technique

This law is the basic yet most often used law in the electrical and electronics world.

Which must be remembered at all cost.

But few of you might have difficulty in remembering things so, this technique is for you guys.

First, draw a triangle divided into three parts like shown in the fig. below

Triangle technique to remember ohm's law

If V and I are given to you and you have to find the value of R, then take R (on the left side) equals to V divided by I (On the right side).

ohms law3
R = V/I

Similarly, if I & R are given and you have to determine V, take V (on the left side) equals to I multiplied with R (on the right side).

ohms law2 1
V = I*R

But it is best suggested to memorize the V = IR relation and derive other variables from this relation.


  • Voltage regulators are the most commonly used application of ohms law.
  • Electric heaters


Ohms law comes with several limitations which restrict its use in many applications.

  1. It doesn’t work with unilateral networks. Unilateral networks consist of unilateral elements such as a diode, transistor, etc.
  2. It also not applicable to non-linear networks. As in non-linear elements, the relation between voltage and current is not linear. This means the value of resistance varies with variation in current or voltage.

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