You cannot present your science fair project without a good level of background knowledge. Furthermore, starting your project with reading and research will give you a good opportunity to write an educated hypothesis. In these experiments, you should speculate whether or not fruits could be used as a battery and which fruits have the least and most electric current. Use a wide range of resources for your project, including library articles and books and academic Internet websites.
Purchase a wide selection of fruits ahead of your experiment, including citrus fruits. Make sure you write a prediction for each fruit before you perform a test for electric current. Set your ammeter to measure microamps in order to show the electric current within the fruit. Push the two probes of the ammeter into the fruit, making sure they are roughly two inches apart and do not touch each other within the fruit. Write down the resulting reading for each fruit in a log book and clearly label. Make sure you wipe the ammeter probes with a paper towel in between testing each fruit.
Once you have your data, and you know which fruits have the least and most electric current, you can repeat your experiment design for the viewing audience and science fair judges on the day of the fair. Select three fruits to use for the demonstration, such as the fruits with the least and most current and a mid-range, low current fruit. Add some patter and showmanship to your demonstration by getting different people to show guess whether they think each fruit will or will not have electric current.
Although your science fair display demonstration will provide your audience a clear idea of your fruit electricity experiment, you should also prepare a speech to explain to people why different fruits have electric current within them. Explain to your audience that citrus fruits, in particular, have a relatively high level of current within them because of their acidic content. Show your confidence and depth of knowledge by inviting questions from your viewers once you have finished your main speech.