An electric current, when it flows through a metal in the presence of a magnetic field, produces an electric voltage perpendicular to the direction of both the current itself and the lines of force of the magnetic field.
When an electric charge moves in a magnetic field, a deflecting force acts on it. It is on this principle that the work of such experimental installations as the synchrophasotron is based, which are widely used in research in the field of elementary particle physics: in them, charged particles are caught in a toroidal (donut-shaped) magnetic trap and fly in a circle inside it. On a small scale, this effect is used in the device of a microwave oven – in it electrons, circulating in a magnetic field, produce microwave radiation that warms up food.
Imagine that there is a piece of conducting wire on the table in front of you, and the magnetic field is directed perpendicular to the plane of the table top. If a current is passed through the wire, the magnetic field will cause the charges inside the wire to deflect in one direction (to the right or left of the direction of the current, depending on the orientation of the magnetic field and the polarity of the charges). Moving away from the direction of rectilinear movement inside the conductor, the charges will accumulate in the border zone until the forces of mutual electrostatic repulsion between them, arising from the Coulomb’s law, balance the deflecting force of the magnetic field on the current. After that, the current will flow rectilinearly again, however, an electrical potential difference will appear on the conductor in a plane perpendicular to both the current direction and the direction of the magnetic field lines, caused by the redistribution of electric charges in the conductor cross-sectional plane, and the magnitude of this potential difference will be proportional to the current strength and intensity magnetic field.
The first transverse electric voltage arising under the influence of an external magnetic field, according to the above scheme, was measured in 1879 by Edwin Hall. He realized that the direction of the voltage vector will depend on which charges – negative or positive – are the current carrier. And, as a result of the experiments, Hall was the first in the world to clearly demonstrate that electric current in metals is created by the directional movement of negatively charged electrons. And before this experiment, scientists doubted both the polarity of the charge-carriers of the current, and about whether the magnetic field acts on charged particles inside the conductor or on the stationary structure of the conductor itself.
More than a century has passed since Hall’s experiments, and the German physicist Klaus von Klitzing (b. 1943) discovered a quantum-mechanical analogue of the Hall effect, for which he was awarded the Nobel Prize in Physics in 1985.