This project turns a lemon into a voltaic battery and demonstrates how chemical energy changes into electrical energy. Cut out 2 inches of copper wire. Straighten a large paper clip and cut off 2 inches. Gently squeeze and roll a whole lemon to internally release the juice. Be sure the peel doesn't rupture. Pierce the two electrodes---the copper wire and paper clip---into the lemon. The electrodes should be very close but not touching each other. Your lemon battery cell is ready. Touch the wires (electrodes) to feel some current. Create several such cells and connect the positive and negative electrodes in a circuit using insulated copper wires and a small device such as a light emitting diode (LED) or a tiny low-voltage bulb. The acid in the lemons will generate a very small amount of electric current although the voltage is significant, 0.7 volts from each lemon.
Roll and soften the lemon and cut a slit big enough to slide a penny in. Leave half the penny out. Carefully pierce a hole with a nail to hold the nail in place. You have the two copper and zinc electrodes, and the acidic lemon juice as the electrolytic solution. The battery is ready. Use conducting insulated copper wires to connect the lemon battery to an LED. The LED should give a dim glow, since the current generated is very small.
This project measures the pH content and voltage generated by several acidic fruits such as orange, grapefruit, lemon and lime. The hypothesis is that the most acidic fruit will generate the most amount of electricity. Use fruits close in size and in the same room at the same room temperature. Cut the fruit in half. Hold a pH meter above and press the "collect" button to collect the pH reading. Take several readings for accuracy. Repeat this with all fruits and save all the halves. The next step is to measure the voltage generated using a milli-voltmeter kit. Follow the directions on the kit to create a bio-battery as in Sections 1 and 2. The circuit this time contains a milli-voltmeter that measures the voltage for each fruit cell. Record the readings of pH and voltage and plot bar graphs for the two parameters for each fruit. Lemon should generate the highest voltage, indicating the most amount of electricity, as it has the highest acidic content.
Present your project results along with the importance of studying bio-electric sources such as a lemons. Mention that nonrenewable energy resources are being used up and it is necessary to research alternative ways of generating electricity. Point out that astronauts in space and countries with a shortage of electricity sources can use the principle behind these projects.