Line of force
Encyclopedia
A line of force in Faraday
's extended sense is synonymous with Maxwell
's line of induction. According to J.J. Thomson, Faraday usually discusses lines of force as chains of polarized particles in a dielectric, yet sometimes Faraday discusses them as having an existence all their own as in stretching across a vacuum. In addition to lines of force, J.J. Thomson—similar to Maxwell—also calls them tubes of electrostatic induction
, or simply Faraday tubes. From the 20th century perspective, lines of force are energy linkages embedded in a 19th century unified field theory that led to more mathematically and experimentally sophisticated concepts and theories, including Maxwell's equations, electromagnetic waves, and Einstein's relativity.
. In Einstein's relativity, there is no ether, yet the physical reality of force is much weaker than in the theories of Faraday.
Historian Nancy J. Nersessian
in her paper "Faraday's Field Concept" distinguishes between the ideas of Maxwell and Faraday:
considered the physical reality of the lines of force as a possibility, yet several scholars agree that for Faraday their physical reality became a conviction. One scholar dates this change in the year 1838. Another scholar dates this final strengthening of his belief in 1852. Faraday experimentally studied lines of magnetic force and lines of electrostatic force, showing them not to fit action at a distance models. In 1852 Faraday wrote the paper http://books.google.com/books?id=yzgLAAAAYAAJ&pg=PA407&lpg=PA407&dq=%22On+the+physical+character+of+the+lines+of+magnetic+force%22&source=bl&ots=vuhrFRrROv&sig=Kpi1IOwE_8KRnZ1QnWokVgMgkHU&hl=en&ei=QJfzTKqLFI-6sQOKtqTCCw&sa=X&oi=book_result&ct=result&resnum=3&ved=0CCIQ6AEwAg#v=onepage&q=%22On%20the%20physical%20character%20of%20the%20lines%20of%20magnetic%20force%22&f=false"On the Physical Character of the Lines of Magnetic Force"] which examined gravity, radiation, and electricity, and their possible relationships with the transmission medium, transmission propagation, and the receiving entity.
took an agnostic approach in his mathematization of Faraday's theories. This is seen in Maxwell's 1855 and 1856 papers: "On Faraday's Lines of Force" and "On Faraday's Electrotontic State". In the 1864 paper "A Dynamical Theory of the Electromagnetic Field
" Maxwell gives scientific priority
of the electromagnetic theory of light to Faraday and his 1846 paper "Thoughts on Ray Vibrations". Maxwell wrote:
". There is a pressure at right angles to a tube of force of one half the product of the dielectric and magnetic density. If through the growth of a field the tubes of force are spread sideways or in width there is a magnetic reaction to that growth in intensity of electric current. However, if a tube of force is caused to move endwise there is little or no drag to limit velocity. Tubes of force are absorbed by bodies imparting momentum and gravitational mass.
2. Magnetic lines of force will never cross one another.
3. Parallel magnetic lines of force traveling in the same direction repel one another. Parallel magnetic lines of force traveling in opposite directions tend to unite with each other and form into single lines traveling in a direction determined by the magnetic poles creating the lines of force.
4. Magnetic lines of force tend to shorten themselves. Therefore, the magnetic lines of force existing between two unlike poles cause the poles to be pulled together.
5. Magnetic lines of force pass through all materials, both magnetic and nonmagnetic.
6. Magnetic lines of force always enter or leave a magnetic material at right angles to the surface.
[From Partha Sarathi Tripathy]
Michael Faraday
Michael Faraday, FRS was an English chemist and physicist who contributed to the fields of electromagnetism and electrochemistry....
's extended sense is synonymous with Maxwell
James Clerk Maxwell
James Clerk Maxwell of Glenlair was a Scottish physicist and mathematician. His most prominent achievement was formulating classical electromagnetic theory. This united all previously unrelated observations, experiments and equations of electricity, magnetism and optics into a consistent theory...
's line of induction. According to J.J. Thomson, Faraday usually discusses lines of force as chains of polarized particles in a dielectric, yet sometimes Faraday discusses them as having an existence all their own as in stretching across a vacuum. In addition to lines of force, J.J. Thomson—similar to Maxwell—also calls them tubes of electrostatic induction
Electrostatic induction
Electrostatic induction is a redistribution of electrical charge in an object, caused by the influence of nearby charges. Induction was discovered by British scientist John Canton in 1753 and Swedish professor Johan Carl Wilcke in 1762. Electrostatic generators, such as the Wimshurst machine, the...
, or simply Faraday tubes. From the 20th century perspective, lines of force are energy linkages embedded in a 19th century unified field theory that led to more mathematically and experimentally sophisticated concepts and theories, including Maxwell's equations, electromagnetic waves, and Einstein's relativity.
Historical origin & differences in field theories
Lines of force originated with Michael Faraday, whose theory holds that all of reality is made up of force itself. His theory predicts that electricity, light, and gravity have finite propagation delays. The theories and experimental data of later scientific figures such as Maxwell, Hertz, Einstein, and others are in agreement with the ramifications of Faraday's theory. Nevertheless, Faraday's theory remains distinct. Unlike Faraday, Maxwell and others (e.g., J.J. Thomson) thought that light and electricity must propagate through an etherAether theories
Aether theories in early modern physics proposed the existence of a medium, the aether , a space-filling substance or field, thought to be necessary as a transmission medium for the propagation of electromagnetic waves...
. In Einstein's relativity, there is no ether, yet the physical reality of force is much weaker than in the theories of Faraday.
Historian Nancy J. Nersessian
Nancy J. Nersessian
Nancy J. Nersessian is the Regents' Professor and Professor of Cognitive Science at the Georgia Institute of Technology. Her work tends to be in the areas of the philosophy of science, the history of science, and the psychology of science.-Works:...
in her paper "Faraday's Field Concept" distinguishes between the ideas of Maxwell and Faraday:
The specific features of Faraday's field concept, in its 'favourite' and most complete form, are that force is a substance, that it is the only substance and that all forces are interconvertible through various motions of the lines of force. These features of Faraday's 'favourite notion' were not carried on. Maxwell, in his approach to the problem of finding a mathematical representation for the continuous transmission of electric and magnetic forces, considered these to be states of stress and strain in a mechanical aether. This was part of the quite different network of beliefs and problems with which Maxwell was working.
Views of Faraday
At first FaradayMichael Faraday
Michael Faraday, FRS was an English chemist and physicist who contributed to the fields of electromagnetism and electrochemistry....
considered the physical reality of the lines of force as a possibility, yet several scholars agree that for Faraday their physical reality became a conviction. One scholar dates this change in the year 1838. Another scholar dates this final strengthening of his belief in 1852. Faraday experimentally studied lines of magnetic force and lines of electrostatic force, showing them not to fit action at a distance models. In 1852 Faraday wrote the paper http://books.google.com/books?id=yzgLAAAAYAAJ&pg=PA407&lpg=PA407&dq=%22On+the+physical+character+of+the+lines+of+magnetic+force%22&source=bl&ots=vuhrFRrROv&sig=Kpi1IOwE_8KRnZ1QnWokVgMgkHU&hl=en&ei=QJfzTKqLFI-6sQOKtqTCCw&sa=X&oi=book_result&ct=result&resnum=3&ved=0CCIQ6AEwAg#v=onepage&q=%22On%20the%20physical%20character%20of%20the%20lines%20of%20magnetic%20force%22&f=false"On the Physical Character of the Lines of Magnetic Force"] which examined gravity, radiation, and electricity, and their possible relationships with the transmission medium, transmission propagation, and the receiving entity.
Views of Maxwell
Initially, MaxwellJames Clerk Maxwell
James Clerk Maxwell of Glenlair was a Scottish physicist and mathematician. His most prominent achievement was formulating classical electromagnetic theory. This united all previously unrelated observations, experiments and equations of electricity, magnetism and optics into a consistent theory...
took an agnostic approach in his mathematization of Faraday's theories. This is seen in Maxwell's 1855 and 1856 papers: "On Faraday's Lines of Force" and "On Faraday's Electrotontic State". In the 1864 paper "A Dynamical Theory of the Electromagnetic Field
A Dynamical Theory of the Electromagnetic Field
"A Dynamical Theory of the Electromagnetic Field" is the third of James Clerk Maxwell's papers regarding electromagnetism, published in 1865. It is the paper in which the original set of four Maxwell's equations first appeared...
" Maxwell gives scientific priority
Scientific priority
In science, priority is the claim and recognition of first discovery or theory. Fame and honors usually go to the first person or group to publish a new finding, even if several researchers arrived at the same conclusion independently and at the same time....
of the electromagnetic theory of light to Faraday and his 1846 paper "Thoughts on Ray Vibrations". Maxwell wrote:
Faraday discovered that when a plane polarized ray traverses a transparent diamagnetic medium in the direction of the lines of magnetic force produced by magnets or currents in the neighborhood, the plane of polarization is caused to rotate.
The conception of the propagation of transverse magnetic disturbances to the exclusion of normal ones is distinctly set forth by Professor Faraday in his "Thoughts on Ray Vibrations." The electromagnetic theory of light, as proposed by him, is the same in substance as that which I have begun to develop in this paper, except that in 1846 there were no data to calculate the velocity of propagation.
Tube of force
Maxwell changed Faraday's phrase of lines of force to tubes of force, when expressing his fluidic assumptions involved in his mathematization of Faraday's theories. A tube of force, also called a tube of electrostatic induction or field tube, are the lines of electric force which moves so that its beginning traces a closed curve on a positive surface, its end will trace a corresponding closed curve on the negative surface, and the line of force itself will generate an inductive tubular surface. Such a tube is called a "SolenoidSolenoid
A solenoid is a coil wound into a tightly packed helix. In physics, the term solenoid refers to a long, thin loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electric current is passed through it. Solenoids are important because they can create...
". There is a pressure at right angles to a tube of force of one half the product of the dielectric and magnetic density. If through the growth of a field the tubes of force are spread sideways or in width there is a magnetic reaction to that growth in intensity of electric current. However, if a tube of force is caused to move endwise there is little or no drag to limit velocity. Tubes of force are absorbed by bodies imparting momentum and gravitational mass.
Magnetic curves
Early on in his research (circa 1831), Faraday calls the patterns of apparently continuous curves traced out in metallic filings near a magnet magnetic curves. Later on he refers to them as just an instance of magnetic lines of force or simply lines of force. Eventually Faraday would also begin to use the phrase "magnetic field".Properties
1. Magnetic lines of force are continuous and will always form closed loops.2. Magnetic lines of force will never cross one another.
3. Parallel magnetic lines of force traveling in the same direction repel one another. Parallel magnetic lines of force traveling in opposite directions tend to unite with each other and form into single lines traveling in a direction determined by the magnetic poles creating the lines of force.
4. Magnetic lines of force tend to shorten themselves. Therefore, the magnetic lines of force existing between two unlike poles cause the poles to be pulled together.
5. Magnetic lines of force pass through all materials, both magnetic and nonmagnetic.
6. Magnetic lines of force always enter or leave a magnetic material at right angles to the surface.
[From Partha Sarathi Tripathy]
Other relevant papers
- Faraday, Michael, "Thoughts on Ray Vibrations", Philosophical Magazine, May 1846, or Experimental Researches, iii, p. 447
- Faraday, Michael, Experimental Researches, Series 19.