# What is the Elementary Charge?

Level 2 (without higher mathematics)

The elementary charge is a physical constant and is the smallest, freely existing electric charge in our universe. The elementary charge is denoted by the letter $$e$$. It has the following exact value:

Value of the elementary charge
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• The unit of the elementary charge $$e$$ is coulomb or also ampere-second:

Unit of elementary charge
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• The charge occurs quantized in nature. That means: All other electrically charged bodies carry a multiple of the elementary charge. If the body carries the charge $$Q$$ (magnitude), then $$Q$$ is composed of $$N$$ elementary charges:

Each charge is a multiple of the elementary charge
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• Quarks have a fraction of the elementary charge, but do not occur freely in nature.

• The value of the elementary charge can be determined, for example, using the Millikan's oil drop experiment. A more accurate method of measuring the elementary charge exploits the quantum Hall effect and Josephson effect. In one experiment the von Klitzing constant $$R_{\text K}$$ is determined and in the other experiment the Josephson constant $$K_{\text J}$$. With the help of these two constants the value of the elementary charge can be calculated:

Elementary charge using quantum Hall effect and Josephson effect
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• In our universe, the elementary charge determines how strongly elementary particles attract and repel each other.

• The elementary charge cannot be annihilated. The charge is preserved in our universe.

The following table lists some particles and what charge they have.

Table : Charge values of different particles
ParticleCharge
Electron$$-e$$ (Definition)
Proton$$e$$
Positron$$e$$
Neutron$$0$$
Down-Quark$$-\frac{1}{3}\,e$$
Up-Quark$$\frac{2}{3}\,e$$ 