Field strength

The field strength is a field size in field theories, which is used for describing the four fundamental forces of physics. In theoretical physics, the field strength is defined as the curvature of a gauge potential. Some introductory texts define the electric field strength and the gravitational field strength in more descriptive, but not a general manner about the power effect that the field strength of a specimen. The spatial distribution and temporal evolution of the field strength is derived from the field equations that represent the relationship between field strength, interactions within the considered physical system and external source terms, such as charges, streams or masses. In classical field theories, field strengths are described mathematically by vectors or tensors or more generally by differential forms. Especially for the characterization of alternating electric fields - - Occasionally, the amount or the rms value of a field strength vector referred to as field strength. In quantum field theories, field strengths are treated as quantum mechanical observables and therefore represented as operators.

Operational definition

The operational definition (and thus the practical test specification ) of the field strength is based on the action of force exerted by the field on a test specimen. The field strengths of the weak and the strong interaction are not directly measurable quantities, so there is no operational definition for them.

Electric field strength

Wearing a body at rest the charge Q and experiences an electric force, then there is at this point the electric field strength

The electric field strength can be given in units of newtons ( ) per Coulomb ( ) or V () per meter ():

Magnetic field

The name of the vector electromagnetic field quantities is historical not consistent with the otherwise uniform use of the term field strength. The magnetic analogue of the electric field strength is not the magnetic field strength, but called the magnetic flux density size. Therefore, physically meaningful in the electromagnetic field strength tensor, but linguistically inconsistent summarized the electric field strength and the magnetic flux density, the physical quantities. Some authors also differ from the IUPAP recommendation and use of the term "magnetic field strength".

The magnetic flux density is defined by the Lorentz force experienced by a charge Q, which moves at the speed in a magnetic field:

The SI unit of tesla is the unit with the letter T:

Gravitational field strength

The gravitational field strength is the size, which is obtained by dividing the force acting in a gravitational field force on a test mass by the mass of the test mass:

For the gravitational field, the gravitational field strength is the same at a location under certain conditions, such as the acceleration of gravity valid at this location.

The unit of the gravitational field strength, can be given as the accelerator, in meters per second squared () or, in the interpretation of the field of force in Newtons per kilogram ():

The field strength of a calibration curve as potential

In modern field theories, such as the Yang-Mills theory, it is the field strength is not operationally defined, but mathematically derived from the fundamental equations of the theory. In these theories, the field strength is defined as the curvature of a gauge potential. By this definition, the field strength at a given gauge potential is uniquely determined. The reverse mapping of the field strength for the gauge potential, however, is not unique, the effect and the field strength are invariant under gauge transformations of the gauge potential.

Since the electromagnetic field strength and the gravitational field strength are directly measurable until the 1960s, the field strength than the physically most relevant field size was considered. Today, however, many consider the gauge potential field theorists over the field strength than the more fundamental quantity. One reason is physical effects such as the Aharonov -Bohm effect, which can only be described by the magnetic vector potential and not by the field strength tensor. Also, the fundamental for the formulation of gauge theories gauge symmetries expressed only at the level of the calibration potentials and not at the level of field strength.