If you suffer a power outage that leaves you in the dark, and your flashlight is out of batteries, you might find the energy to power the bulb in your refrigerator. An orange, lemon or lime can act as a battery, and while a single one might not generate enough voltage to illuminate an LED bulb, several wired in series will.
Citrus fruits can do this because they contain citric acid, an electrolyte that allows electricity to flow. The power actually comes from the electron exchange between a pair of electrodes that you insert in the fruit pulp. For the exchange to be powerful enough to do anything useful, you need a strong conducting medium, and citrus fruits — especially lemons — have that in spades. The citric acid in citrus fruits is an electrolyte that allows electricity to flow between electrodes made from dissimilar metals.
Whether you know what they are or not, your body uses electrolytes constantly to transmit the electrical impulses that make life possible. An electrolyte is a fluid that contains free ions. They can come from dissolved salts or from acids that donate free positively charged hydrogen atoms — protons — to solution.
Because the ions can move around freely, they gravitate toward a source of opposite charge and away from a source of like charge. You don't need much to make a battery out of a lemon or a lime. The electrolyte is already present in the fruit, so all you have to add is a pair of electrodes and some conducting wire to connect them.
The electrodes need to be made from dissimilar metals to create a potential difference between them. Zinc and copper are a good pair. In a citric acid solution such as exists inside a lemon, copper produces extra electrons.
They flow through the electrolyte to the zinc, where they build up. When you connect the electrodes with a wire, the charges travel through the wire back to the copper electrode, thus completing the circuit. A galvanized nail makes a great zinc electrode. Use a piece of gauge electrical wire or a penny for the copper electrode. If you opt for a penny, make sure it was minted before Later pennies are made mostly from zinc. Many people may think it's amazing that a simple piece of produce can conduct electricity.
As it turns out, that's not the whole story. There are many types of electrical conductors. These include traditional electrical conductors, such as the copper and silver wires that are used to run electrical currents in homes and buildings, and ionic conductors, which can power electricity via free moving ions. Organic material, such as human tissue or the potato in your science experiment, are ionic conductors that create ionic circuits.
Electrolytes — chemical compounds that create ions when they are dissolved in water — in these materials do all of the work. They don't conduct electrons [as traditional electrical conductors do] [ How Do Batteries Work?
An ionic conductor contains positive and negative charges — otherwise known as charged ions — that move freely when they come into contact with a voltage. These ionic solutions are called electrolytes and can be found in every living thing. Because of this, technically, any fruit or vegetable could become an ionic conductor, but some are better at it than others.
This is also why salt water or unfiltered tap water are better ionic conductors than filtered fresh water.
The best food battery is any fruit or vegetable that has high levels of superconductive ions, such as potassium or sodium, and the proper internal structure to create a working current.
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