Georg Simon Ohm (1787-1854), a German physicist, in 1826 experimentally determined the most basic law relating voltage and current for a resistor. Ohm's work was
initially denied by critics.
Born of humble beginnings in Erlangen, Bavaria, Ohm threw himself into electrical research. His efforts resulted in his famous law. He was awarded the Copley Medal in 1841 by the Royal Society of London. In 1849, he was given the Professor of Physics chair by the University of Munich. To honor him, the unit of resistance was named the ohm.
What is Ohm's Law?
Ohm's Law deals with the relationship between voltage and current which states that the potential difference (voltage) across an ideal conductor is directly proportional to the current through it.
Fig.No.1: Ohm's law
$$ V \propto I $$
The constant of proportionality is called the "resistance", R. Ohm's Law is given by:
$$V = IR$$
where $V$ is the potential difference between two points which include a resistance $R$. $I$ is the current flowing through the resistance.
Ohm's Law can be used to solve simple circuits. A complete circuit is one which is a closed loop. It contains at least one source of voltage, and at least one potential drop i.e., a place where potential energy decreases. The sum of the voltages around a complete circuit is zero.
An increase of potential energy in a circuit causes a charge to move from a lower to a higher potential (ie. voltage). Note the difference between potential energy and potential.
A decrease of potential energy can occur by various means. For example, heat lost in a circuit due to some electrical resistance could be one source of energy drop.