Lemon Battery

A lemon, two metals, and some wire: that is all it takes to build a working battery and light a bulb with fruit power.

Safety:

Do not eat the lemons afterward — the metal ions make them unsafe. Wash hands after handling the metals.

Materials

2 to 4 lemons
A copper coin, strip, or wire
Galvanized (zinc-coated) nails
Insulated wire with alligator clips (or bare wire)
An LED (red works best)
A multimeter (optional but great)

Procedure

Prepare the lemons

Roll each lemon firmly on the table to break up the pulp inside — this frees the juice that will carry the current.

Insert the electrodes

Push a copper strip and a zinc nail into each lemon about 2 cm apart, without letting them touch inside. These are your two electrodes.

Measure one lemon

Touch the multimeter probes to the copper (+) and zinc (−) of one lemon and read the voltage.

Chain them in series

Wire the lemons in series: connect the zinc of one to the copper of the next. Measure the total voltage across the chain.

Light the LED

Connect the LED's long leg to the final copper and short leg to the final zinc. If it does not glow, add another lemon.

What to observe

One lemon measures about 0.8 to 1.0 V on a meter.
Two lemons in series read roughly double; in parallel the voltage stays the same.
An LED glows dimly with three or four lemons chained together.

Why it happens

This is a galvanic cell: the zinc nail oxidizes (loses electrons) while hydrogen ions in the lemon juice gain them at the copper electrode, and the acidic juice conducts ions between the two. Each lemon gives about 0.9 V. Chaining lemons in series adds their voltages ( $V_{total} = V_1 + V_2 + \dots$ ) — which is exactly why a 9 V battery is six small 1.5 V cells stacked inside one case. The LED needs roughly 2 V to glow, so three or four lemons in series do the job.

Try variations

Try potatoes, apples, or pickles — which fruit or vegetable gives the highest voltage?
Compare copper-zinc with copper-copper or zinc-zinc. Why does one pair fail?