Elementary charge
Overview
The elementary charge, usually denoted by e or sometimes q, is the electric charge carried by a single proton, or equivalently, the magnitude of the electric charge carried by a single electron, which has charge −1 e. This elementary charge is a fundamental physical constant. To avoid confusion over its sign, e is sometimes called the elementary positive charge.
Fundamental Constant
The elementary charge e is one of the fundamental constants of nature. It is the smallest amount of charge that a particle can have as observed in the universe. The value of the elementary charge is approximately 1.602176634×10−19 coulombs. It is included in the International System (SI) of Units as one of the seven fundamental constants. This reflects its universal nature and importance in the physical sciences.
Quantization of Electric Charge
The concept of the elementary charge is closely related to the principle of quantization of electric charge. This principle, first proposed by the physicist Robert A. Millikan, states that the electric charge of any particle is an integer multiple of the elementary charge. This means that the charge q of any particle is given by q = ne, where n is an integer. This quantization of charge is a fundamental property of the universe and is one of the cornerstones of quantum mechanics.
Role in Atomic Structure
The elementary charge plays a crucial role in the structure of atoms. In an atom, the protons in the nucleus carry a positive charge equal to the elementary charge, while the electrons orbiting the nucleus carry a negative charge of the same magnitude. The balance of these charges is what keeps the atom stable. The number of protons (and hence the number of elementary charges) in an atom determines the atomic number and hence the identity of the element.
Role in Electromagnetism
In the field of electromagnetism, the elementary charge is fundamental to the concept of electric charge, which is a property of subatomic particles that determines their electromagnetic interaction. The force between two charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them, as stated in Coulomb's Law. The elementary charge is also central to the definition of the ampere, the SI unit of electric current.
Role in Quantum Electrodynamics
In quantum electrodynamics, the elementary charge is related to the coupling constant that determines the strength of the interaction between charged particles and the electromagnetic field. This interaction is responsible for phenomena such as the creation and annihilation of particles, and the deflection of particles in a magnetic field.