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What is the Elementary Charge?

Answer #1

Level 2 (without higher mathematics)
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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.

    Electric positive / negative charge - attraction and repulsion
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    Attraction and repulsion of charged particles.
  • 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\(\frac{2}{3}\,e\)