Elementary charge

The elementary charge, denoted as e, is a fundamental physical constant that represents the smallest unit of electric charge that is considered indivisible in the context of quantum mechanics. It is a key component in the study of electromagnetism, particle physics, and quantum field theory.

Definition

The elementary charge is defined as the magnitude of the electric charge carried by a single proton, or equivalently, the negative of the charge carried by a single electron. It is a fundamental constant of nature and is used as a basic unit of charge in the SI system.

Value

The value of the elementary charge is exactly 1.602176634 × 10⁻¹⁹ C. This value is fixed by the definition of the coulomb, which is based on the elementary charge itself. The elementary charge is a dimensionless quantity in the context of natural units, where it is often set to 1 for simplification in theoretical physics.

Historical Context

The concept of the elementary charge was first introduced by George Johnstone Stoney in 1874, who coined the term "electron" to describe this fundamental unit of charge. The measurement of the elementary charge was significantly refined by Robert A. Millikan in his famous oil-drop experiment in 1909, which provided the first accurate determination of the charge of the electron.

Role in Physics

The elementary charge plays a crucial role in the Standard Model of particle physics, where it is a fundamental parameter in the electromagnetic force, one of the four fundamental forces of nature. It is also a key component in the quantum electrodynamics (QED) theory, which describes how light and matter interact.

In atomic physics, the elementary charge is essential for understanding the structure of atoms, as it determines the electrostatic forces between protons and electrons. In solid-state physics, it is important for the study of semiconductors and superconductors, where the movement of charge carriers is a fundamental process.

Applications

The elementary charge is used in various applications across different fields of science and technology. In electronics, it is fundamental to the operation of transistors, diodes, and other semiconductor devices. In chemistry, it is crucial for understanding ionic bonds and electrochemical reactions.

In metrology, the elementary charge is used in the definition of the ampere, which is one of the seven base units in the SI system. The ampere is defined by taking the fixed numerical value of the elementary charge to be 1.602176634 × 10⁻¹⁹ when expressed in the unit C, which is equal to A·s, where the second is defined in terms of the cesium frequency.

See Also

• Electron
• Proton
• Coulomb
• Quantum mechanics
• Electromagnetism
• Standard Model

External Links

• [Elementary Charge on NIST](https://physics.nist.gov/cgi-bin/cuu/Value?e)
• [Elementary Charge on CODATA](https://physics.nist.gov/cuu/Constants/index.html)