Fruit Batteries
Most recent answer: 9/15/2016
- Anonymous
[see correction below] Batteries work by moving and storing charges - a lot like electricity. In order for a fruit to be a battery, it needs to be able to conduct electricity. You may have learned about acids in school - if you haven't, acids make ions, or charged particles, when put in a solution like water. These charged particles from acids are the same type as the charged particles in electric current, so the fruit that will make the best battery is the one that is most acidic. Another general thing about acids - they tend to taste sour. The stronger the acid in the fruit, the more sour it will taste. Since a lemon is the most sour of the three, it will make the best battery. [or so we once thought]
-[name deleted]
(published on 10/22/2007)
Follow-Up #1: correction
- Wes Carr (age 19)
It sounds like your experiments show that the previous answer was not right.
The reasoning in the old answer was very sloppy. Several parts of the description of the role of electrical charges didn't even quite make sense. The factors which play a role in producing power include the acidity (which plays a role in the chemical reactions at the electrodes), the presence of various other ions (acidity just involves H+ ions), and the permeability of the cell walls, which can block currents. That’s not intended to be a complete list. As a result, it’s unlikely that some simple theory will predict well which complicated material (lemon, potato, ...) will produce the most power.
Whether your answer (more power from the potato) is correct in general or just for particular types of potatoes, etc. is another question.
Anyway, thanks for the correction. I've left the exchange in to inspire other critics.
Mike W.
Lee H
(published on 10/22/2007)
Follow-Up #2: apples vs. oranges
apple,orange,lemon,grapefruit,---this appears opposite of what they should have in regards to Ph correlation ----------Can you explain?????
- dave
lincoln il
Mike W.
(published on 10/22/2007)
Follow-Up #3: alkaline batteries
- Robert Escalante (age 41)
Houston, Texas, USA
Alkaline batteries really do have different chemistry than acidic ones. There’s a useful Wikipedia entry: .
I guess you're right that in an alkaline solution the simple zinc-copper battery could have the same reaction as a commercial alkaline battery:
Zn(solid)+2OH- ->Zn(OH)2(solid)+ 2e-
rather than the reaction
Zn(solid) -> Zn+2 (aqueous)+ 2e-.
However, you'd have to check the reaction potentials to see what's realistic in, for example, a potato.
Mike W.
(published on 10/22/2007)
Follow-Up #4: trust wikipedia?
- JMtB03 (age 14)
Evansville, IN, USA
Mike W.
(published on 12/06/2011)
Follow-Up #5: Fruit-powered Radio Control (RC) Car
- noah (age 13)
OHIO
(published on 01/13/2012)
Follow-Up #6: pH and fruit batteries: data
- Hina (age 41)
Austin, TX
Mike W.
(published on 02/18/2012)
Follow-Up #7: fruit batteries and pH
- Scott (age 45)
Michigan
All your other items were mainly water, with various extras. In them, the different propensities of Zn and Cu to dissolve as ions cause a voltage to build up, driving a current if the circuit is completed. The experience of everybody who has written in, as well as my own limited tests, indicates that pH has little effect on the voltage of these batteries. Since saying the solution is "acid" means pretty much the same thing as saying the pH is low, it looks as if the acid part doesn't play a big role. We were all surprised by that, but those are the facts. I guess the remarks in some of the answers above about alkaline reactions may have something to do with these results.
Here's how you can test if that chlorine matters. Use some distilled water (available at the grocery store) without chlorine. You could try then adding some baking soda or some clear vinegar to change pH without adding chlorine.
Mike W.
(published on 01/27/2013)
Follow-Up #8: weak fruit batteries
- michelle (age 11)
davie,florida,usa
My guess is that your battery just wasn't supplying enough current even for those little diodes. You might try using ten copper electrodes and ten zinc electrodes, wiring all the copper ones together and all the zinc ones together. Keep the copper ones spaced far apart from each other, and the same with the zinc, so that the ion currents inside the fruit from different electrodes don't overlap too much. Don't put the copper and zinc very far from each other. You may need several pieces of fruit.
Mike W.
(published on 02/18/2013)
Follow-Up #9: ammeter for fruit batteries
- Neil (age 55)
Boston, MA, USA
Mike W.
(published on 03/08/2013)
Follow-Up #10: apple batteries beat lemon
- Joep van Walsum (age 17)
Netherlands
Mike W.
(published on 04/23/2013)
Follow-Up #11: permeable potatoes
- X (age 22)
Kolkata,WB,India
That's quite possible. One of our earlier answers discused the permeability issue. One could do various tests, such as comparing lemon juice with a lemon.
Mike W.
(published on 07/26/2013)
Follow-Up #12: fruit juice battery experiment
- Loretto E (age 40)
Riverside CA
That's a wonderful experiment! Thanks for settling that question.
We still don't know the reason, but you and your daughter eliminated one of our wrong ideas.
Mike W.
(published on 11/01/2015)
Follow-Up #13: current from battery
- James A (age 13)
Lake butler,Florida,U.S.A
It's ok because the currents from all the batteries go through the RC car as they loop around.
Unfortunately our question-asking function doesn't allow posting pictures. It's very limited because allowing more flexibility makes it easier for hackers to mess up the site.
Mike W.
(published on 09/15/2016)