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.