# Lemon Battery

It is possible to make a simple battery from a lemon. This is a very simple experiment and requires no expensive or complex equipment.

A basic battery consists of two different metals suspended in an acid solution. For our experiment a lemon (citric acid) or vinegar (acetic acid) works well. The lemon juice is the electrolyte through which electrons will travel from one metal to the other.

### Electric Potential

All metals have something called electric potential which is basically a measure of how easily they give up electrons (or attract electrons if the value is below zero). For example calcium has a potential of +2.20 volts, whereas gold has a potential of -1.10 volts. Using two metals, the difference between potentials can be used to create a flow of electrons. For example the flow of electrons between calcium and gold equates to a potential difference of 3.30 volts (= +2.2 – -1.1). This would be an expensive battery – therefore look at the potential voltage of some common metals – Aluminium (+1.30), Zinc (+0.758), and copper (-0.345) then we see it is possible to make a cell of around 1 volt very cheaply.

### Lemon Battery

A good fresh and juicy lemon works best, but a potato or apple can easily be used. Cut a shallow slit in one side of the lemon and insert either a copper coin (sometimes coins thought to be copper are in fact not pure copper so use copper wire instead if necessary), and in the other side insert a galvanised nail (which is coated with zinc) or metal paperclip. The copper coin/wire is the +ve electrode of the cell, and the galvanised nail is the -ve electrode. The electrons will travel from the -ve electrode through the electrolyte to the +ve electrode – thereby creating an electric current. Below is an illustration of an aluminium-copper lemon cell.

If you measure the voltage across the lemon cell then it will be just under 1 volt – not enough to do anything useful. However if you connect a few of these lemon cells together in series (+ve to -ve, +ve to -ve, and so on as shown above) then a higher voltage battery can be built. Once the voltage is over 2-3 volts the battery of lemon cells can be used to light up (not very brightly) an LED. Four lemon cells connected in series will typically generate around 3.5 volts.

### Vinegar Battery

An alternative to the lemon battery is to use empty film cannisters filled with vinegar, with a zinc nail and some copper wire dangled through holes in the lid into the liquid. Two of these can be wired in series and used to power a small LCD clock or calculator.