Electricity from fruit (cont'd)

Hi Sophia. You didn't mention what grade you are in, but you need to be rather careful with terminology like "conducted energy better" and "conduct more energy". You are expressing yourself rather vaguely about some observations you made. Trying to answer "why" something happens that you haven't clearly enunciated, can confuse and mislead you :-)

The role of the fruit juice in this case is probably mostly to provide a conductive electrolyte. That leads me to a thought: Have you ever eaten orange segments? Suppose you've peeled an orange, and you've eaten most of it, and now you have two segments left. Do you think you'll get the same or different results if you stick both of your probes into the same segment, versus sticking one probe into one segment and one into the other, being careful not to puncture the membranes separating the two segments?

Regards,

A. Hi Steve. Almost anything is possible, surely including charging a phone using fruit batteries...

What voltage does a phone charger for the phone in question provide? What amperage does it provide? Hint: my questions provide the advice you asked for on how to go about it.

Regards,

A. Hi Sherryn. You're halfway there in finding that some things will support this battery action if the probes are inserted into them and some will not. But the issue or principal that your son should be getting is what is actually happening that accounts for the electricity flowing ...

If a single metal electrode is placed into acid it will slightly dissolve into the acid, much like salt or sugar will dissolve into water to a given equilibrium point (if you add too much salt or sugar it just settles on the bottom as a syrup). As the metal slightly dissolves into positively charged ions in the solution (atoms less one or more electrons) this leaves excess electrons on the metal electrode, and they attract ions back and reform metal, and this is what comprises the "equilibrium".

But if you put both copper and zinc rods into the same solution, when the dissolved copper ions (atoms of copper less two of their electrons) happen to reach the zinc electrode, they will steal two electrons from the zinc metal and become copper atoms again, plated out onto the surface of the zinc. Why copper has this stronger thirst/affinity for those electrons than zinc may be beyond your son's level, but the principal of what is happening probably isn't.

As mentioned, when the copper atom dissolved, it left those two electrons on the copper electrode, and they will now flow through the wiring to get over to the zinc electrode to balance things out. This flow of electrons through the wiring is what we call electricity. The reaction will continue until the zinc is completely covered with copper and the surface of the two electrodes is the same metal, so nothing further can happen and the "battery" is dead.

Butter is oil rather than water, and will not support the dissolving of metal into ions. So it's not that it's an insulator, it's that metal can't ionize into it. Similarly, dry salt crystals cannot support metal ionizing into it. Good luck.

Regards,

A. Hi Ignatius.

1. Zinc is gray and metallic looking. Galvanized nails, galvanized roofs, and boat anodes all have a zinc surface.
2. I don't know what circuit you are speaking of, but I have been speaking of a "fruit powered battery", where a piece of copper and a piece of zinc stuck into the fruit comprise the battery.
3. Yes, you can use an unripe orange.
4. Your circuit will be unable to light even the tiniest penlight flashlight bulb. You would probably need a dozen fruit batteries wires in parallel to light that penlight battery, or a few to light even a small LED per the youtube video we referenced.

Luck & Regards,

A. Hi Iliyan. That question was answered in detail several times on this page already. Please try to read and understand the explanations, then to re-phrase your question so we can resolve any remaining uncertainty you have.

Also, try to think carefully what the word "amount" means to you because I can think of at least two different meanings (alkalinity and pH) related to "the amount of acidity", and many meanings (voltage, current, power, energy) regarding electricity. Good luck.

Regards,

A. Hi Paola. The basic problem is that it's the two metals which generate the voltage, not the potato. All the potato does is provide a conductive liquid path. But I would guess that, yes, if you use a strong salt solution, with the metals placed close together, the resistance of the circuit is lower and you should be able to get more current to flow, and the LED to glow more brightly. With more current flowing, the battery will go dead sooner though.

Regards,

A. Hi Emili. Please look at the youtube video of the lemon battery on this page. The person making the video found that he had to wire 4 lemon batteries in series to light a small LED.

Regards,

A. Hi Kimberly. I hope you tried these materials repeatedly because it would be foolish for him to carefully explain why something is true if it's not true :-)

But assuming the results are repeatable, it means some of the materials conduct sufficient electricity to run the clock (it probably takes very very little) and some do not. Anything with a little water in it probably works, and things that are dry, or based on oil rather than water, do not. If you happen to have an electrical meter you could measure the resistance of each of these objects.

Regards,

A. Hi Brokson. Sorry, but it's not the fruit or vegetable which you choose that determines the voltage, but the two metals. I'm not happy to have to tell you that, but it is what it is :-)

Regards,

A. Hello Kushi. Copper has a much stronger pull on electrons than zinc has: about 1.0 volts worth. So if you put a piece of copper and a piece of zinc into a fruit, a meter would record about 1.0 volts between them as some of the electrons in the zinc metal are pulled through you wiring and over to the copper metal. If you put two such batteries in series (connecting the positive end of one to the negative end of the other, much as you stack 1-1/2 volt batteries in various electronic devices, you would get about 2.0 volts between them. If you stack 4 of these 1.0 volt batteries you get about 4.0 volts.

Regards,

We'd love to give credit for this graphic explaining Ohm's Law (A = V / Ω) but we see it on many websites with no hint of whose work it actually was :-(

Hello Jemima. The voltage of the battery will remain unchanged because it is a function of the two metals employed (copper and zinc). But the maximum current that metal plates of a given size can produce is increased because the boiled potato is a better conductor. The practical implication is that more power can be generated in a given space, i.e., it's a more practical packaging method/design for the battery.

The biggest problem is that this corrosion of zinc and copper isn't really "free" energy because it costs more energy to make zinc and copper from ore, i.e., to un-corrode them, than you can get from corroding them like this. Batteries can be a convenient storage device for energy, but they don't actually produce energy, they just release a portion of the energy that was stored in them.

Regards,

Hi -- just a quick note to thank you so much for taking the time to provide such a thoughtful and articulate answer to my boiled potato question, and so quickly! It's really wonderful that you've been keeping this thread and information going for so long. Cheers from Oz!

A. Hi Edward. For reasons that are beyond grade 7 level and maybe my level, zinc attracts electrons more strongly than copper does. So if you put the two metals into a conductive solution but not touching each other, and you attach a wire between them, electrons will flow through the wire from the copper to the zinc. As this happens, the copper atoms on the surface of the copper, having lost their electrons, do not remain a metallic solid, but dissolve as positively charged copper ions into the solution (much like salt or sugar dissolve into water). The positively charged copper ions migrate through the solution until they reach the zinc electrode and are able to regain their electrons and come out of solution, as copper plates onto the zinc electrode. The process of electrons flowing through the wire from the copper to the zinc, and copper ions dissolving into solution and traveling to the zinc electrode continues until the zinc is completely covered with copper and the process dies out.

You do not have to use zinc and copper, you can use any two metals as long as one has a stronger attraction for electrons than the other. You may have heard of carbon-zinc batteries, nickel-cadmium batteries, etc. But zinc and copper are readily available, relatively cheap, and the difference in attraction of electrons is large, so they generate a good voltage (about 1.1 volts).

A. Hey, Emmanuel, I don't think you can. What leads you to believe that it can be done?

Regards,

And what unit of measure are you looking for "moisture content" in?

Electrical conductivity in this context requires there to be liquid, and for that liquid to have ions in it. The liquid is usually taken as a given, so conductivity is often used as a measure of how many ions there are. If the liquid dries up and the ions turn into solid salt, it would pretty much lose conductivity, but it's doubtful you would need to measure the current to be able to notice that.

Hi David. Good to hear. Let us know what you find out about that. Thanks.

Regards,

A. Hi Tenzing. No, every experiment does not require a control. A control is used for "what would have happened if I didn't add chemical 'X', or do procedure 'Y', or how do I account for the presence of 'Z'?".

Imagine that your daughter's teacher says "Iodine might be a terrific conductor of electricity. Please prove/disprove it by measuring the conductivity of a beaker of tap water and then, because pure iodine is a bit hard to get and so very little is needed, add iodized salt to a 2nd beaker of water and measure its conductivity". It would probably immediately occur to you that the salt rather than the iodine might explain the increase in conductivity. In this case you might decide to add non-iodized salt to a 3rd beaker of water and measure its conductivity. That 3rd beaker is your control -- it lets you determine whether the tiny amount of iodine really explained the increased conductivity, or whether the salt you inadvertently added to get the iodine in there was the important factor in the increased conductivity.

Sometimes the 'control' is implicit or understood: When you measure the conduction of the fruit or vegetable with the meter leads say 1" apart, an implicit or understood control is that when the meter leads were 1" apart in air the conductivity was for practical purposes zero, so the leads being in the fruit is what produced the conductivity. Good luck.

Regards,

A. Hi again. Yes, you need a multimeter, and you need to measure resistance. We probably need to understand exactly what resistance, conductance, resistivity, and conductivity mean. The cute little graphic further up the page shows the relationship between voltage, current, and resistance. Voltage is measured in volts, current is measured in amperes (amps), resistance is measured in ohms. If you know two of the three, the third is easily solved for from the relationship Amps = Volts/Ohms. Conductance is the reciprocal of resistance, and is expressed in mhos; mho doesn't really mean anything, it's just ohm spelled backwards as a reminder. If the resistance of something is 10 ohms, its conductance is 1/10 mho; if it's resistance is 1/20 ohm, its conductance is 20 mho.

Resistance and conductance are a measure of an entire system: the resistance read on the meter is the resistance of the copper or zinc wires plus the fruit of vegetable. The way it works is the multimeter has a battery in it and when you set it to ohms or resistance the battery is used; it produces a voltage, say 1-1/2 volts, which runs through the wires and the fruit and the meter needle ... the amount of current that can flow through the system against this resistance causes the meter needle to move, and the scale of ohms is painted under the different possible needle positions.

You perhaps shouldn't even use the words resistivity and conductivity, but they are properties of a material rather than a measurement of a system. Rubber is a very high resistivity, low conductivity material. And copper is a very low resistance, high conductivity material. But even with a low resistivity material like copper wire, if you make the wire 100X as long its resistance will be 100X as high.

In practice you are going to touch your meter leads together and note that the resistance is essentially zero. That is your 'control' that accounts for the wires so you are measuring just the resistance of the fruit. Then you are going to put the meter leads into the fruit or attach them to pennies or copper wires you put in the fruit. You should always place the leads or wires approximately the same distance apart in each fruit because, as mentioned, resistance increases proportionally to distance.

Regards,

A. Hi. If you use a digital meter it's probably "auto-ranging" -- it may shift the range up or down by itself and just give you the answer in ohms or megaohms (millions of ohms). If you use an analog meter (one with a needle) it's more fun and a better learning experience. Pick whatever resistance range you wish, touch the two leads together and 'zero' it if necessary. Then attach to your two probes in the fruit. If it reads very close to zero, try to move down to a lower range so the needle is nearer the middle; if it reads close to infinity, try to move up to a higher range so it reads nearer the middle. Resistance is measured in "ohms", so no conversion is necessary -- the meter reads in ohms. However, you may find that the meter range says 'X1000" or "X100,000" or "Megaohms" (X1,000,000), so you have to multiply what the needle says by that factor.

Regards,

A. Hi again. Unfortunately this lesson seems beyond 4th grade level and your daughter may have little real concept of anything even after all your efforts. The main issue is that resistance and conductivity have no meaning except as a relationship between voltage and current, neither of which she has been introduced to (it seems from here), and neither of which she has any concept of (it seems from here). It's no wonder it confuses you, let alone a 4th-grader :-)

But maybe some things can be made just a bit clearer regardless. First, to be a stickler, I must note that you did not read 15 ohms or 17 ohms or 22.5 ohms so you must not word it that way, so I crossed it through. You were on a scale that read thousands of ohms, so you read 15,000 ohms, 17,000 ohms, and 22,500 ohms. You understand that, but it's also important to only say it that way. Secondly, everything is relative, and you mustn't say that 1/22500 is "close to zero"; small resistors in electronic circuits often have a resistance a thousand times greater than your fruits, and therefore a conductance 1000X smaller, and it's still not close to zero :-)

Lastly, the units we use in describing conductance is mhos, not ohms, which I'll now try to explain...

Back to what I alluded to earlier, resistance is a relationship between voltage (Volts) and current (Amps): that relationship is R = V/A.
So an "Ohm" is also or actually a Volt per Amp. We could say the resistance of your grapefruit was 22,500 Ohms or we could say that resistance was 22,500 Volts per Amp.

Conductance, as you realize, is the reciprocal of resistance: so C = A/V.
Thus, conductance is measured in Amps per Volt rather than Volts per Amp, and since Ohms means Volts per Amp we can't use that unit of measure to describe conductance, we must use mhos. Excellent work even if it wasn't fully understandable!

Regards,

A. Hi again. It is correct to say that conductance is the reciprocal of resistance and to express it in mhos.

Her conclusions are that apples are more conductive than grapefruits, and conductance decreases when the probes are further apart. She has disproven her hypothesis that fruits or vegetable with the most water and the highest acidity are more conductive: because the data she recorded contradicts that hypothesis, and all it takes is one example to show that the hypothesis is demonstrated to be incorrect. However, she should not go too far and claim that fruits & vegetables with less water or lower acidity are more conductive because a single example does not prove the general case.

Regards,