The material combined with particle of molecule. When heat produce the molecule of materials vibrating. So when current flow through the conductor it resist to flow current. Thus create voltage to the end line of the conductor. As like water flow upper side to lower layer. Like current flow upper voltage to lower voltage. When current goes through the conductor due to resist the flow of electron it vibrate the molecule and produce heat. That mean so many obstruct its resist so much thus so mean heat. It's meaning heat is a condition of Ohm's Law.

In the above discussion, there is voltage increase the flow of electron increase. We know the flow of electron is current for a definite time interval. So it is seen that the voltage and current are proportional and vice-versa.

So we can write, I ∞ V, V denotes voltage and I denotes current.

The behave of resist the flow of electron is known as resistance. It is done by resistor which symbolic presentation is R.

On the other hand, Current resist by Resistor. That means so much resistance it resist to flow of current so much. So the relation between current and resistance is inverse proportional.

We can write, I ∞ 1/R

Together above two equation,

                            I ∞ V/R

If current measure in 1 A, voltage measure in 1 V and resistance measure in 1 Ω.

So we can write the proportional constant is also unity.

Now we can write I = V/R

                            or, V = IR.

This is the Ohm's Law which states the relation between current, voltage and resistor.

Here the practical link of Ohm's law is given below. Here Rheostat is used; is another kind of variable resistor.