A penny and a galvanized nail serve as the electrodes here. Each one moves electricity into or out of the lemon, turning a piece of fruit into a working battery.

A lemon works as a simple battery because it contains citric acid, which carries an electric charge between two different metals. The acid reacts with each metal differently, and that difference creates a flow of electrons — the tiny charged particles that make up electricity. Push a copper piece and a zinc strip into a lemon, then connect the two metals to a small LED. The question is whether the current the citric acid drives through that circuit is strong enough to make the LED glow. It's the same basic idea behind commercial batteries, just with fruit instead of a sealed case.

A lemon contains citric acid, which carries an electric charge between two different metals — the same basic idea behind commercial batteries. Push a penny and a galvanized nail into a lemon and the acid reacts with each metal differently. That unequal reaction pushes electrons from one metal to the other, creating a flow of current. Connect your lemon battery to a small LED and see whether that current is strong enough to make it glow.