Ohm's Law - (Concept)

All of us must have seen when a torch is used for several weeks, its light becomes dim. We say that its cells have become weak. What does it mean? It means that the potential differences across the terminals of the cells have reduced. When such a cell is used in a torch, less current flows through the bulb, and hence, it produces less light. So, we can say that the electric current passing through an element depends on the potential difference applied across it.
George Simon Ohm, a German physicist performed a series of experiments to determine the exact relationship between the potential difference and electric current which is stated by the law named after him.
Ohm’s law states that the electric current flowing through a metallic wire is directly proportional to the potential difference V, across its ends provided its temperature remains the same.

Or in other words,

$$
\begin{aligned}
& V \alpha I \\
\Rightarrow & \frac{V}{I}=\text { constant }=R \\
\Rightarrow & V=I R
\end{aligned}
$$

where,
R is a constant for the given metallic wire at a given temperature and is called its resistance.

Resistance:-
- Resistance is the property of a conductor to resist the flow of charges through it. Its SI unit is ohm, represented by the Greek letter $\Omega$. According to Ohm's law,

$$
R=\frac{V}{I}
$$

- If the potential difference across the two ends of a conductor is 1 V and the current through it is 1 A, then the resistance R, of the conductor is $1 \Omega$.

$$
1 \mathrm{ohm}=\frac{1 \text { Volt }}{1 \text { Ampere }}
$$

- So, for a given potential difference, $i \notin \frac{1}{R}$

i.e., for a given potential difference, the current is inversely proportional to the resistance. So, we can say that the higher is the resistance, lower is the current.