A: a) Voltage in essence is a measure of the amount of work done per unit charge as it moves through a circuit. Now, voltage can be differentiated into two types depending on how the unit charge moves. If the unit charge is moving between two points of a component/conductor/circuit, then that is a potential difference. If the unit charge is moving round a complete circuit, then that is electromotive force, or emf.

b) Current is defined as the rate of flow of charge, or amount of charge flowing through a circuit per unit time.

- Two magnets attracting each other
- An apple falling from a tree
- Charges produced by friction
- None of these