# What is the Elementary Charge?

## Answer #1

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**

The unit of the elementary charge \(e\) is

*coulomb*or also*ampere-second*:**Unit of elementary charge**Formula anchor $$ \begin{align} \mathrm{C} ~=~ \mathrm{As} \end{align} $$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**Formula anchor $$ \begin{align} Q ~=~ N \, e \end{align} $$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**Formula anchor $$ \begin{align} e ~=~ \frac{2}{R_{\text K} \, K_{\text J}} \end{align} $$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.

Particle | Charge |
---|---|

Electron | \(-e\) (Definition) |

Proton | \(e\) |

Positron | \(e\) |

Neutron | \(0\) |

Down-Quark | \(-\frac{1}{3}\,e\) |

Up-Quark | \(\frac{2}{3}\,e\) |