Current is the rate of flow of electric charge. Voltage across an electrical component is needed to make a current flow through it.

Components are chosen based on factors including working properties, environmental impact, function, manufacturing processes etc. It is important to choose a component fit for purpose.

Current transfers energy around circuits. Circuit components have various properties that can be measured and then used to make circuits for control.

Metals have many uses due to their properties which include strength, malleability and also the conduction of electricity .

A chemical cell produces a voltage until one of the reactants is used up. In a hydrogen-oxygen fuel cell, hydrogen and oxygen are used to produce a voltage, and water is the only product.