Overview of the key terms and skills related to electric charge, including how to calculate net charge.
|Elementary charge (
|Smallest possible unit of charge. Equal to the charge on one proton or the magnitude of charge on one electron, which is
|Sum of the charges on an object.
|SI unit for electric charge. The amount of charge transferred in
How to calculate net charge
There are two kinds of electric charge, positive and negative. On the atomic level, protons are positively charged and electrons are negatively charged.
Although the mass of a proton is much larger than that of an electron, the magnitudes of their charges are equal.
If an object has more protons than electrons, then the net charge on the object is positive. If there are more electrons than protons, then the net charge on the object is negative. If there are equal numbers of protons and electrons, then the object is electrically neutral.
When charge is transferred between objects, it’s only the electrons that move. An electron can’t be broken into smaller pieces, so charge always changes in multiples of the elementary charge. This property of electrons means that charge is quantized and the charge on any object must be an integer multiple of the elementary charge. An object’s charge can be
, etc., but not , etc.
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For deeper explanations of electric charge, see our video triboelectric effect and charge.
To check your understanding and work toward mastering these concepts, check out the exercise on quantization of charge in experimental data.