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Find out which battery terminal is positive and which is negative

Suitable For

Grade 4



Time Required

 <1 Hour



What’s it about?

How would you know which terminal of a battery is positive and which is negative if it were not indicated on the battery? Say for instance you needed to jump start a car, but its battery is so old you can no longer make out which terminal is which. Before you can safely connect the cables to the battery terminals, you might need to perform a simple test like the one in the following science experiment to know which one is which:

Topics covered

Conductor, Electrolyte

What will I need?


Procedure (Method)

Unfortunately, this section is only available in the e-book version of the project.

How does it work?

Unfortunately, this section is only available in the e-book version of the project.

In this science experiment, the liquid in the potato acts like an ‘electrolyte’ allowing current to pass through the potato. This causes the liquid to react with the electrical current. The wire connected to the positive terminal of the battery (Anode) causes the potato liquid to form very small, sometimes invisible, bubbles around the wire when the ‘protons’ react to the chemicals in the potato.

A much more noticeable green substance is formed around the negative wire as the negatively charged electrons react with the potato’s chemicals. Within a few minutes it is possible to determine which of a batteries’ terminal is which. This simple principle could also be applied to find the polarity of a car battery.

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This particular science project can be found in any of the following Experiland e-books:

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