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In $$1827$$, Georg Simon Ohm, a German physicist, conducted various experiments and formulated Ohm's law. The law describes the relationship between potential difference and the current flowing in a metallic wire.

Ohm's law states that,
At a constant temperature, the steady current '$$I$$' flowing through a conductor is directly proportional to the potential difference '$$V$$' between the two ends of the conductor.
Mathematically, it is written as

$I\phantom{\rule{0.147em}{0ex}}\mathrm{\alpha }\phantom{\rule{0.147em}{0ex}}V$

Hence,

$\frac{I}{V}=\mathit{constant}$

(or)

$I=\left(\mathit{constant}\right)\phantom{\rule{0.147em}{0ex}}V$
The value of the proportionality constant found in the above equation is $\frac{1}{R}$.

Therefore,

$\begin{array}{l}I=\frac{1}{R} V\\ \\ V=\mathit{IR}\end{array}$

Where $$V$$ is the potential difference, $$I$$ is the current flowing through a conductor, and $$R$$ is the resistance of a material. The resistance is constant for a material (e.g., copper) at a given temperature.

The above equation can also be written as,

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

In terms of units, the resistance $$R$$ of a conductor is said to be $$1\ ohm$$ with a potential difference of $$1\ volt$$, causing the current of $$1\ ampere$$ to flow through the conductor. Then,

$\mathit{1}\phantom{\rule{0.147em}{0ex}}\mathit{ohm}=\phantom{\rule{0.147em}{0ex}}\frac{\mathit{1}\phantom{\rule{0.147em}{0ex}}\mathit{volt}}{\mathit{1}\phantom{\rule{0.147em}{0ex}}\mathit{ampere}}$

The current flowing through a resistor is inversely proportional to its resistance.

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

When the resistance is doubled, then the current is cut in half. Sometimes, in practical applications, the current needs to be increased or decreased in an electric circuit. In such cases, a rheostat is used to change the resistance in the circuit.
Variable resistance is a component used to regulate current without changing the voltage source.