Barlow's law
Encyclopedia
Barlow's law was an incorrect physical law
proposed by Peter Barlow in 1824 to describe the ability of wires to conduct electricity
. It said that the conductance of a wire varies inversely with the square root of its length and directly with the square root of its cross-sectional area, or:
where G is conductance, l is the length of the wire, A is the cross-sectional area of the wire, and k is a constant
specific to the material of the wire.
In 1827, Georg Ohm
proposed a different law, stating that the resistance
of a wire varies directly with its length and inversely with its cross-sectional area. Experiments eventually proved Ohm's law
correct and Barlow's false.
Barlow undertook his experiments with the aim of determining whether long-distance telegraphy
was feasible, and believed he proved that it was not. The publication of Barlow's law delayed research into telegraphy for several years, until Joseph Henry
and Philip Ten Eyck disproved it in 1831.
Physical law
A physical law or scientific law is "a theoretical principle deduced from particular facts, applicable to a defined group or class of phenomena, and expressible by the statement that a particular phenomenon always occurs if certain conditions be present." Physical laws are typically conclusions...
proposed by Peter Barlow in 1824 to describe the ability of wires to conduct electricity
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
. It said that the conductance of a wire varies inversely with the square root of its length and directly with the square root of its cross-sectional area, or:
where G is conductance, l is the length of the wire, A is the cross-sectional area of the wire, and k is a constant
Physical constant
A physical constant is a physical quantity that is generally believed to be both universal in nature and constant in time. It can be contrasted with a mathematical constant, which is a fixed numerical value but does not directly involve any physical measurement.There are many physical constants in...
specific to the material of the wire.
In 1827, Georg Ohm
Georg Ohm
Georg Simon Ohm was a German physicist. As a high school teacher, Ohm began his research with the recently-invented electrochemical cell, invented by Italian Count Alessandro Volta. Using equipment of his own creation, Ohm determined that there is a direct proportionality between the potential...
proposed a different law, stating that the resistance
Electrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...
of a wire varies directly with its length and inversely with its cross-sectional area. Experiments eventually proved Ohm's law
Ohm's law
Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points...
correct and Barlow's false.
Barlow undertook his experiments with the aim of determining whether long-distance telegraphy
Electrical telegraph
An electrical telegraph is a telegraph that uses electrical signals, usually conveyed via telecommunication lines or radio. The electromagnetic telegraph is a device for human-to-human transmission of coded text messages....
was feasible, and believed he proved that it was not. The publication of Barlow's law delayed research into telegraphy for several years, until Joseph Henry
Joseph Henry
Joseph Henry was an American scientist who served as the first Secretary of the Smithsonian Institution, as well as a founding member of the National Institute for the Promotion of Science, a precursor of the Smithsonian Institution. During his lifetime, he was highly regarded...
and Philip Ten Eyck disproved it in 1831.