Ohm’s Law: The Ultimate Guide

Ohm’s Law is the fundamental law of Electrical Engineering which explains the relationship between voltage and current on any resistor. In this ultimate guide, you will learn ABC to XYZ of this Law.

George Simon Ohm was a German Physicist behind this law. Let’s start our learning with the statement:

The current passing through any resistor is directly proportional to the amount of current flowing through it.


V ∝ I


V: Voltage

I: Current

How George Simon Experimentally Verified Ohm’s Law

Ohm’s Law was not derived mathematically, it was determined experimentally by George.

Let’s repeat this experiment to develop an insight about the Law.

Consider a 1k ohm resistor across which a variable DC source is connected.
Tip: A variable DC Source can provide variable values within the desired level.

Now, When we apply 1 V to the resistor, a current of 1 mA flows through it.

By increasing the voltage level to 2V the current rises with an equal rate and changes 2mA.

The same happens for 3V –> 3mA and so on.

Finally, for 1-10V we can express our results which are expressed here in tabular form:



We can generalise our observations:

Doubling the voltage (V) doubles current (I), Tripling the V triples I and so on.

We can also perform the experiment in our lab and can practically verify the same. However, we might expect little difference in the results due to practical conditions and quality of our resistors.

Recently I performed this experiment in my lab. Here I am sharing the results which I achieved:


One can compare the results of both tables to observe that there are only minor difference which occured because I was using a carbon resistor with Golden tolerance Band.

Point to Remember: A gold band represents tolerance of 5%.

Circuit Diagram: An Introduction to Symbols


The above diagram provides a pictorial arrangement for the previously done experiments.

Symbols of Battery: The symbol of battery with script 1-10 and an arrow represents that we are using variable DC supply.

Zigzag Resistor: The zigzag symbol with the script of 1kΩ represents the resistor across which we are checking our results.

Wires: The connecting lines are the wires which represent the connection between circuit components.

How to Solve Circuits Using Mathematical Relationship

We previously explained the three basic electrical quantities which are:

  1. Voltage (V)
  2. Current (I)
  3. Resistance (R)

In Electrical Engineering we usually come across numerical problems and complex problems where two of these parameters are given and we usually have to find the third one. All the possible cases involving these three values are given here with their solution.

Example 1: A 10V source in connected across a 5k Resistor. Find the value off of current flowing through the circuit.

Solution: I = V/R = 10V/5k = 2mA

Example 2: A 20 ohm Resistor has 10A flowing through it. Find the value of supplied voltage.

Solution: V = IR = 10A*20 ohm = 200V

Example 3: An unknown resistor is connected across the 5V source and a current of 2.5 mA is flowing through it. Find the value of the resistor.

Solution: R = V/I = 5V/2.5mA = 2kΩ



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