Variables in Generating Electricity from Fruits

[Panina]

Hello

Having trouble determining the variables for Generating Electricity from Fruits. We are going to compare three fruits: Orange, Apple and Kiwi

would the Independent Variable be Cooper and Zinc electrodes you insert into the fruit
Would the Dependent Variable be the Orange, Apple and Kiwi
Would the controlled Variable be the multi meter equipment used to measure the voltage?

Thanks,
Nina

[theborg]

Nina,

Welcome to the forum and thank you for your question. determining the variables in an experiment can be quite tricky. Here is a link to the SB guide on variables for additional reference and research:
https://www.sciencebuddies.org/science- ... bles.shtml

The independent variable is the thing you want to change to see if it has an effect on the dependant variables.

For your experiment the independent variable is the type of fruit, or more specifically the acidity levels (which is different for each fruit). The fruits acid level determines the voltage it can generate, so voltage is your dependent variable. Everything else is part of the environment and experiment setup and must be controlled so are called control variables, so be sure to use the same type and sizes of electrodes and use the same multi meter, etc...

Please post back with any other questions.

[Panina]

Thank you for you help, I was switched around (as you hinted), as I was using the Fruit as the dependent variable, as I was observing the changes....and then the electrodes as the independent variable, because instead of copper electrodes I could use coins....

But now I can see, that the experiments is About Generating Electricity....and the explanation of my variables is important...so I am observe the level of voltage that each fruit can generate to determine which one is a better conductor of electricity.

Thank you, now I have to explain to my son how we should continue researching to have right Hypothesis.

Nina

[rmarz]

Panina - There is another important variable to measure, that is energy. How much power (voltage and current) is the fruit producing. While the acidity level will interact with the dissimilar metal electrodes and produce a measurable voltage, that voltage is very different and independent of the current generated. In fact, the electro-chemistry is such that the voltage is likely pretty constant in each fruit, and a higher voltage in one fruit does not suggest it is generating more power. The power, or energy, will be highly influenced by the surface area of the electrodes. I don't mean to confuse you, but simply measuring voltage, in itself, may not lead to the expectations you might have made in your hypothesis. You might want to have a subset of experiments within each fruit, where you determine the output energy as affected by surface area of the electrodes.

Rick Marz

[theborg]

The important thing to remember is that you should only have one independent variable for each experiment. As Rick suggests, you could change surface area of electrodes, or your suggestion of changing electrode type (i.e. coins) but then that becomes your variable and you then should test all different electrodes in each fruit. This would make your hypothesis about which electrodes worked best.

I'm assuming that you are using the Science Buddies project on this subject. If not, I would recommend looking it up in the project idea section of this forum. The link to it is in my signature block below.

[bradleyshanrock-solberg]

Just to reinforce the prior comment.

It is possible to run experiments for multiple variables, but it's a hard enough problem that even professionally, people only do it when they have no other choice, or when trying each variable one at a time requires simply too many experiments (and thus too much time/money, when a more complex process but single experiment can cope with multiple forms of variation). For this reason science fair projects normally only have one independent variable, especially in the lower grade ranges, and if you become an engineer or scientist it will be bleep they teach after you've mastered the usual one-variable approach.

Also, even with one variable, you need to run an experiment more than once to be sure of your results. Again, the reasons why don't get taught usually until college (Statistics) but the concept isn't hard. The first try could be not very much like the normal result. Doing it twice gives you some idea of how much difference you can get with the same experiment. Three times lets you know which of the first two is more "normal". Adding more tries costs more in time and often money, and each trial does less to bring down your uncertainty about how accurate your result is, but for a science fair project, planning three trials of each test is a pretty good middle ground. Doing so adds a lot to the confidence of your conclusions while only adding a moderate amount of extra work.