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Science project: Lemon juice as electricity source



A discussion started in 2001 and continuing through 2017 . . .

(2001)

Q. Does lemon juice work in a clock as energy? If so, how? This is for a science fair project. I am in the 4th grade.

Evan B [last name deleted for privacy by Editor]
- Slidell, Louisiana


Potato Clock



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VOM meter

(2001)

A. Not exactly, Evan. Let's compare to a battery: Flashlight batteries that you buy at a store have a zinc case, with a carbon rod in the center, and they are filled with a conductive black glop.

The electricity in a battery is a result of the difference in the electrochemical potential between the zinc and the carbon, combined with the fact that the conductive black glop allows ions to travel from one electrode to the other. Your lemon battery has a zinc covered nail (galvanized nail) instead of a zinc case, a copper penny instead of a carbon rod, and lemon juice as the conductive solution instead of the black glop. The lemon juice is not the source of the electricity, the system is -- two different metals and a conductive solution connecting them.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(2006)

Q. Hello we are crying and we want to know why do we get less voltage from a lemon than from an apple by using an analog multimeter. Maybe we are doing something wrong; can you help us? We are from 8th grade and we can't find an explanation why we get so little voltage from the lemon compared to other fruits, why did we get more from the apple, is the apple acidic?

Rebecca B [last name deleted for privacy by Editor]
student - Guatemala City, Guatemala


(2006)

A. You are probably not using identical electrodes in the lemon, Cousin Rebecca. The voltage depends mostly on the two different metals that the electrodes are made of. It does not depend very much on the electrolyte (the apple juice or lemon juice). Try again using the same electrodes in the lemon as in the apple.

It may not be there forever, but here is a great YouTube video on lemon batteries --^

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


January 28, 2008

A. I found that all citrus fruits will power a small light bulb. Also if you cut two slits in to your fruit, stick a nail in one and a copper penny in the other slit, they will act as the plus and minus sides of a battery. The nail will be coated in zinc, and the penny will be made of copper. This will only work if the two metals are not touching. (Sometimes pennies aren't made with pure copper, so for best results, use a real copper wire). The nail and penny are scientifically entitled electrodes. The fruit juice is scientifically identified as an electrolyte. The flow from the minus to the plus side is the flow of electrons. The penny and nail are the conductors, which allow electrons to flow through them.

Electricity is produced by the flow of electrons. The electron flow is sometimes produced by chemical reactions. Some of these reactions including this are the zinc from the nail, the copper from the penny, and the citric acid from the fruit.

An average lemon should produce about 0.7 volts of electricity. An average orange will produce approximately 0.6 volts of electricity. A grapefruit will probably produce around 0.6 to 0.7 volts. A lime on average will produce about 0.5 volts of energy.If you want to measure the voltage, connect a volt meter to the wires to see how many of each fruit you will need to power the bulb's voltage. Keep adding fruit until you get the right amount of volts, then connect the light. Results may vary, due to the difference of acids in different fruit, and brand of fruit.
Allie and Kaylie

Allie A [last name deleted for privacy by Editor]
- Alden, New York



November 22, 2008

Q. HEY I'm MARIA I TESTED MANY MANY FRUITS.
I TESTED THEM WITH A COMPUTER. AND IT TAKES 100 LEMON TO TURN ON A COMPUTER. I KNOW THIS EXPERIMENT IS AWESOME YOU SHOULD DEFINITELY TRY IT. I'm A SCIENTIST I LOVE FINDING NEW THINGS AND THIS EXPERIMENT IS ONE OF THE BEST ONES PROVEN, BY ME OF COURSE.

I have a question. What would be the hypothesis for this project?

Maria G [last name deleted for privacy by Editor]
- Florida


December 8, 2008

A. Hi, Maria. Your hypothesis should be an educated guess about something, and it should be testable. Ideally it should involve independent variables you can alter and dependent variables that change in a cause & effect way when you alter the independent variables.

So it would be nice if your experiment was more quantitative rather than qualitative. In other words, answering a yes/no question like "is 100 lemon batteries enough to run a computer" is quite impressive, but not quite as satisfactory a science experiment as saying "I believe that the voltage available from lemon batteries is cumulative, additive, and directly proportional to the number of batteries" and then graphing the number of batteries vs. the voltage you generate. If you accept this suggestion, just leave out "I believe that" and you have your testable hypothesis.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



November 26, 2009

Q. I am doing a Science Fair project off of something I saw on TV. It was a lemon stereo I am using galvanized nails, copper, wire and radio , oh and a plug that looks kind of like what you would use to start up your car when the battery dies but it is a lot smaller and is not connected.I need help! Please respond ASAP! Please I'm in the 7th grade. Thanks for anything you can do.

KayLynn C [last name deleted for privacy by Editor]
- Columbus, Georgia


November 2009

? Hi, KayLynn. Unfortunately I did not see the TV show that you did, and I have no idea what you're talking about. Sorry! Hopefully another reader will remember it.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



July 28, 2012

Q. Can I use citric acid solution instead of lemons?

Naomi Ishihara
- New Zealand


April 2017

A. Hi Naomi. Yes. No problem.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



December 16, 2012

Q. Does temperature affect the amount of voltage of a lemon?

Gene [last name deleted for privacy by Editor]
- Los Angeles


December 17, 2012

A. Hello Gene.Please look to the "galvanic series", the "seawater series", and the "Nernst Equation" and see if there is any reference to temperature. I don't think there is.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



March 24, 2015

Q. Hi I really need help, I was testing the effect of temperature on the voltage of fruit batteries, and all of the fruits increased in voltage as the temperature had increased, but the lemon had not. Is this reasonable, or had I made a mistake in my tests?
Thanks

Mia M.
- New York, NY, USA


March 2015

A. Hi Mia. I would suggest sticking with your results rather than trying to fudge, excuse, or justify them. You didn't say what grade you are in, but I think the essential lesson is how to follow and document procedures, and practice the scientific method, rather than to deeply understand complicated theoretical formulas. So keep a really proper lab book and you should be fine.

My understanding is that temperature doesn't affect the theoretical voltage (standard electrode potential) sufficiently to be measured with the rather casual instrumentation available to students. Rather, it affects peripheral stuff, like current flow, etc., that distort those measurements. I would suggest that if your hypothesis was along the lines of: "Raising the temperature of fruit batteries increases their voltage", your conclusion would be "Inconsistencies is measured results appear to contradict the hypothesis, but were not sufficient for confidence". Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


March 26, 2015

A. Mia,
If any data point is in question, one thing you can do is repeat the trial. Outliers happen, and when they do you report them and then discuss why you decided to leave them out for any charts or calculations that the data is used for. However if the suspected outlier stays consistent, then something else is at work.

It may be above the level of understanding of batteries that's been provided to you, but Ted is right. The voltage is technically only caused by the electrode material, it defines how "much" the electrons "want" to move from one to the other. The actual current flow, or the "speed" at which the electrons are able to move, would be affected by the conditions such as the temperature and choice of electrolyte (in this case, the type of fruit being used).

As for your lemon, further experimentation would normally be called for. I think in your case you probably don't need to, as Ted said this is more about procedure and documenting results. Some of the best science has come out of papers reporting results that were totally unexpected and unexplainable at the time. However, to put forth a hypothesis, I wonder if one might find that the temperature/current relationship is not fully linear. Maybe the increase in current from getting warmer levels off somewhat above a certain temperature. Maybe the lemon is a much better conductor than the others, so the range you tested was within the leveled-off part while for the other fruits you were in the part before the level-off.

Ray Kremer
Stellar Solutions, Inc.

McHenry, Illinois




April 20, 2017

Q. I am doing a lab and I want to know how much volts lemon juice has.

Anoushka Bhatnagar
Raha International School - Abu Dhabi, Dubai


April 2017

A. Hi Anoushka. Lemon juice has the same voltage as any other mild acid: zero. The voltage in the experiment is the difference in electromotive potential between copper (0.34 volts) and zinc (-0.76 volts), i.e., about 1.1 volts. Good luck.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"

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