The lemon battery is called a voltaic battery, which changes chemical energy into electrical energy. The electrodes are placed in a liquid containing an electrolyte, which is a solution that can conduct electricity, to break down the atomic shape of the copper and zinc. Once they are broken down this helps electrons release off of the copper and zinc. These are called electrodes, which are the parts of a battery where electric current enters or leaves the battery. Electrodes permit the electrons to move freely through them. One of the metals contains positive electric charges, while the other contains negative electric charges. In this test the copper is the Anode (+) and the zinc is the Cathode (-).Cathodes are a negatively charged electrode that is the source of electrons entering an electrical device. Anodes are an electrode through which electric current flows into a polarized electrical device The acid in the lemon reacts differently with each of the two metals. These charges create current, which will flow if the battery circuit is finish. Wire conducts the charges, making the circuit complete. The complete electric circuit causes a small amount of electricity to flow, which causes the thermometer to turn on. The battery is made up of two different metals (the zinc plated nail and the copper wire). In a solution of water and an electrolyte, like the acid in the lemon, an excess of electrons collects on one end of the electrodes. At the same time, electrons are lost from the other electrode. Touching the electrodes to your tongue closes the circuit and allows a small electric current to flow. A single lemon produces about .914 of a volt of electricity. One lemon does not have enough electrolytes to turn on the digital thermometer however, 4 lemons produces too much voltage and causes the digital thermometer to not work correctly.
Because Lemons has acid and it can reacted with metal and release electron,so Lemons can Produce Electricity.