Ohm's Law

Every gadget contains circuits inside it.

A scientist “Georg Simon Ohm” in 18th century wanted to know the working of these circuits.

But only batteries were available at that time. So, he started working on batteries.

He started conducting some experiments using batteries.

Ohm started his experiment with the following setup :

The setup had a bulb, a battery and connecting wires of which circuit was made.

When he applied a certain potential difference, some current was recorded.

He saw that on increasing the potential difference,there was an increase in current.

And on decreasing the potential difference, there was a decrease in current.

Ohm then started to take a mathematical approach on his observations.

So, for every value of applied potential difference, he plotted the value of current on a graph paper.

On joining the points on the graph, he got a straight line.

Mathematically, equation of a straight line passing through the origin is given by: y = mx

In our graph, voltage is on y-axis and current is on x-axis.So we can write :

So from the graph we can say as above.

Here this constant ‘R’ is called “Resistance “(R).

From this equation we can infer that as above.

The SI unit of resistance is “Ohm”.

1 ohm is resistance of a circuit when of 1 ampere current flows through it and voltage is 1 volt.

Let us see how resistance affects the flow of current.

Consider in a race in which electrons have to travel from one terminal of battery to other .

Now, the villain of the story comes and stops electrons from moving ahead.

This villain is called “Resistance”. Higher the resistance more is the opposition.

But, there is somebody to help our electrons, which is voltage.

Higher the voltage, easier is for electrons to move.

Let us look at some properties of Resistance.

Resistance is constant only if temperature remains same.

It varies from one material to other.

Some materials are highly resistive to the flow of electrons,while others allow easy flow.

Let’s take a look on the statement of Ohm’s Law and it’s expression.

According to Ohm’s Law: “Current flowing through a wire is directly proportional to potential difference applied across its ends”.

This statement is valid under a constant temperature only.

And the final expressions of Ohm’s law are as above.


Ohm’s law states that current is proportional to applied potential difference.

It is applicable under constant temperature conditions only.

Resistance is the property of any material which opposes the flow of electrons through it. It’s SI unit is ohm.

The End