Reciprocity (electromagnetism)

Reciprocity is an important concept in electromagnetism, which tells us that the properties of an electrical device can be described by swapping the roles of electric current and voltage. This means that if we take two devices that both have wires to carry electricity, and swap their wires, their behaviour should be the same as before. So, it's like if two people are playing a game of tag, but we switch who is 'It' and who is running away. The game is still the same, even though the roles have been swapped.