Science Buddies: "Ask an Expert"

My son is doing a science fair project. Instead of making a fruit/veggie battery, he just wants to measure the electrical resistance of various fruits and compare them to each other.

His procedure has been to stick the leads of his multimeter into each fruit, then record the data shown on the Ohms scale. The problem he is running into is that the potato is showing less resistance than the orange and the lemon. He believes that the orange and the lemon should be less resistant, not more.

He also wants to know if electricity flows more easily through substances with high Ohms measurement (higher resistance) or low Ohms measurement (lower resistance).

Thank you.

Let's look at each question:
1. In my opinion a potato is more dense than either the orange or lemon which might be the reason for it's lower resistance.
2. Electrical current flows better through a substance with low resistance and a worse through a high resistance. This can be expressed by Ohm's law which is I=E/R or Electrical current = Voltage divided by Resistance. Hence. the higher the resistance the less current flows given a constant voltage.
I hope this helps.

Dear nan13,

I agree with the answer that a potatoe is more dense than the lemon/orange and offers the least resistance. In your experiment I would recommend using a voltage measured in a battery experiment and from there calculate the resistance. You can use the formula: I = V/R. I hope this helps, and please let me know if I can provide any additional info.

Jay

Thanks for your replies. Gerry, can you tell us in layman's terms why something that is more dense would have less resistance?

Dear nan13,
I came up with this research for the density of the pototoes being able to be a good conductor of electricity than tomatoes and lemons.

To maximize electrical flow, the matter inside the vegetable should be dense (packed together) and fairly uniform. This creates fewer barriers for the electrons to overcome in their travel from one metal wire to the otherand hence vegetables with gaps, such as lettuce, have lots of air pockets that cannot conduct electricity and thus make poor batteries. Tomatoes and lemons are less dense and have more barriers than potatoes for the flow of electron from one metal wire than the other and hence there is more resistance than the potatoes.

Vegetable Chemical Makeup

The ingredients of the vegetable also play a role. Water and acid make for the best electrical conductors. We're all aware of water's ability to conduct electricity Acid also introduces more charged ions into the material, which have the effect of "pushing" the electrons along in their journey, thus speeding up the current. Vegetables high in potassium make for optimal conductors.

Advantages of Potatoes

Potatoes are considered the best conductors because they are uniformly solid, about 80 percent water and rich in potassium. Other solid vegetables, such as carrots and broccoli stems, can conduct electricity but are not rich enough in potassium to move current very well. Potatoes also represent a good balance of size and density: they are just big and non-dense enough to slow the electrons down without impeding their travel,making them least resistance for the electriacl current to go throuugh it.

I hope this is helpful.

Sincerely,
Jay.

Dear nan13,
Jay has offered an excellent explanation as to why a potato has better electrical conductivity (low resistance). I couldn't have said it better myself.
Regards,
Gerry