Current and Voltage

A current of one amp flows when a charge of one coulomb flows around the circuit per second.

A potential difference of one volt will supply one joule of energy to each coulomb of charge passing around the circuit.

If we imagine coulombs of charge as cans of pop travelling along a conveyor belt, then increasing the current would be like speeding up the belt. On the other hand, increasing only the voltage would be like keeping the speed of the belt the same but putting hot cans of pop onto the belt; each can contains more energy. Increasing the current and voltage at the same time would be like doing both.