Q: How can I develop a hypothesis for this project?
A: Remember that a hypothesis must be something testable; that is, your hypothesis should be a claim that you can then support or refute with evidence from your project. For this project, a common hypothesis is comparing two or more fruits and vegetables and choosing which one you think will provide the most voltage or current. You could also try to test which fruit or vegetable requires the least amount (by volume or mass) to power the same electronic. If you want to stick to one fruit or vegetable, you can play around with the configuration of, and distance between, the electrodes to see what provides the most power.
The following Science Buddies resources may help:
- Writing a Hypothesis: http://www.sciencebuddies.org/science-fair-projects/project_hypothesis.shtml
- A Strong Hypothesis: http://www.sciencebuddies.org/blog/2010/02/a-strong-hypothesis.php
Q: I can't power anything with my battery. How can I fix this?
A: If you are having difficulty powering anything with your battery, you should double check the following for possible issues:
- Make sure your vegetable or fruit is fresh. The longer you use one piece of fruit or vegetable, the more moisture it will lose; a dry fruit or vegetable will not provide power. It helps to pre-soak your fruit or vegetable in water (this is particularly effective with potatoes) and keep the fruit or vegetable in a sealed container during the experiment.
- Your electrodes will also influence how much power you can get from the battery. Make sure they are clean and fully inserted into the fruit or vegetable. Increasing the surface area of the electrodes will also increase the output of your battery. Try using long, flat strips of metal instead of nails, if possible.
- Check the energy requirements of the device you are trying to power. If it requires too much current or voltage, no feasible vegetable or fruit battery will be able to power it. Look for items that run at 3 volts or less and that draw less than 0.5mA. Good choices include a small calculator, a 3 volt radio, a battery-powered timer, or an LED light.
- Often a battery has either sufficient voltage or current to power the device, but not both. It is important that your battery meets both the voltage and current requirements for whatever you are trying to power. Using your multimeter, measure the voltage and current of your battery. If one of those values is lower than what is needed to power the device, try rearranging your battery in a series (to create more voltage) or in parallel (to create more current). Look at the project idea for more instructions on how to do this.
- As with any project dealing with electrical components, check your connections! Just one wire that is poorly connected to something else can keep your entire experiment from working properly.
A: Measuring current can be difficult in more complex circuits. In a battery such as this, you want to "break" the flow of electrons (the current) and insert your multimeter so that the electrons have to flow through the meter. You also want to make sure that your multimeter is set to the right sensitivity to measure amperes (a good start is 200A). This Science Buddies resource helps you learn how to measure current: http://www.sciencebuddies.org/mentoring/project_ideas/Elec_HowToMeasure.shtml.
Q: Does it matter what gauge of wire I use in this experiment?
A: Smaller gauge wire is probably better, but any gauge will work for this experiment. Larger gauge wires generally cause more resistance than smaller gauge wires. For copper, 12-gauge wire will have a resistance of about 1.5-1.7 ohm per 1000 feet of wire, versus about 4.0ohm/1000ft for 16-gauge wire. However, even though 16-gauge wire has twice as much resistance, it is still a very small amount of resistance, especially over the short lengths of wire used in this project.
Q: (Science Buddies Kit) My battery won’t power the calculator, what should I do?
A: First, check your connections, using Figures 3 and 4 in the Project Idea to help you. Circuits are sometimes funny, and sometimes simply taking your battery apart and assembling it again can solve problems. You may find it helpful to label your two voltaic cells "A" and "B," as shown in Figure 3. One alligator clip jumper cable should connect the copper wire from potato A to the galvanized nail in potato B. A second alligator clip pair should connect the copper wire in potato B to the positive battery terminal in the calculator, and a third alligator clip pair should connect the galvanized nail in potato A to the negative battery terminal in the calculator.
You should also use the multimeter to check the voltage being produced by the battery, as described in step 2 of Experiment 1 in the Project Idea. If your battery is out of "juice," it will not power the calculator even if the connections are correct.
Q: (Science Buddies Kit) I accidentally disconnected the wires in the calculator or stopwatch, what do I do?
A: If this happens, find a pair of wire strippers and carefully strip the ends of the wires that were disconnected until you have enough of the wire stripped so that you can twist the wires back together. Tweezers might make it easier to twist the wires together.
If you have other questions about the procedure or need assistance troubleshooting your project or the Experimental Procedure, please post your question in the forum for this kit at Ask an Expert: http://www.sciencebuddies.org/science-fair-projects/phpBB3/viewforum.php?f=54. Our team of volunteer Experts is available to assist. We attempt to reply to questions within 24 hours. Please note that you will need a free Ask an Expert account in order to post questions.