Force field (physics)
A force field in the physical sense, is a field which assigns to each point in space has a field strength. This field strength causes a force on a test body which is in the force field. The force depends on the location and the " charge " of the specimen with respect to the relevant interaction from. If the field strength is caused by the electromagnetic interaction, then the electric charge, the body is then called sample charge. In the gravitational field, it is the mass of the body is, then sample mass.
The force on a test body in a force field is mathematically a vector-valued function of position. Force fields can be represented by means of field lines.
In the literature, the use of the term is not uniform: the term can be understood on the one synonymous with the field strength so that it is the field that exists independently of the presence of a specimen and does not have the dimension of a force; Such a field has to be multiplied by the charge of the specimen, in order to obtain the force on them. Other authors understand by the force field, however, a field function with the dimension of a force from the specimen being used. The addiction is to understand the specimen without retroactive effect of the specimen on the existing field.
Examples
Of an electric field is obtained by multiplying the electric field with the electrical charge of the specimen, a field of force. Analogously in a gravitational field by multiplying the gravitational field strength (ie, the acceleration of gravity ) to the mass of the specimen, the force of gravity. Magnetic charges do not exist, however. Suitable specimens for a magnetic field is a magnetic dipole or a moving electric charge.
If the test specimen in the force field along a path s moves from A to B, while the work is
Performed. Will it along a different path s ' again from B moves back to A, it is the work done W' for conservative force fields at the same W, but can be used for force fields that are no gradient of a potential, such as the magnetic field vary.
In the simplest case, the force field is homogeneous, ie the force is equal in all places. This is an idealization which is a reasonable approximation for example, the gravitational field in the vicinity of the earth's surface, or the electric field between two capacitor plates.
History
Classic field concept from 1830
The term force field was developed around 1830 by Michael Faraday from the observations to electricity and magnetism out and clarified the picture of the field lines. Thus, there is at each point in space a certain field strength, which can be detected and measured by its force on a test specimen. And immediately the gravity was described by a gravitational field. Is caused a field by another body, the source of the field. For that to be replaced as philosophically problematic image viewed from a distance,: A body no longer works through the empty space directly to another one, but creates around itself a field at the location of the other body exerts in turn its effect.
The fact that a field belongs physical reality independent of its source, was shown in 1886 by Heinrich Hertz discovered that free electromagnetic fields exist in the form of waves and spread. 1905 resulted from the special theory of relativity by Albert Einstein, that these fields exist without any material substrate ( "ether" ) in a vacuum and do not spread infinitely fast, but the speed of light. The thought that this would also apply to the gravitational field, led Einstein to general relativity in 1916.
1900 Max Planck made the discovery that the free electromagnetic field can absorb or release its energy only in certain portions. These were later called in 1905 by Einstein as light quanta as photons. This marks the beginning of quantum physics.
Quantum field theory from 1927
From 1927 turned Paul Dirac, Werner Heisenberg, Wolfgang Pauli, inter alia, the rules of quantum mechanics to fields. Thus, the photons are the elementary excitation levels of the free electromagnetic field. Moreover, it follows that photons can exist in " virtual states " that would be prohibited by the classical field equations. In such states, the photon can not be detected directly, but are responsible for all observable electric and magnetic effects. Thus they stand in quantum electrodynamics as exchange particles behind the electromagnetic interaction and call out in particular the Faraday force fields.
The corresponding quantum field for the second force field of classical physics, the gravitational field, called gravitons. It is currently unknown but if they really exist. A satisfactory quantum field theory for gravitation has not been found.