Horseshoe magnetA horseshoe magnet is either a permanent magnet or an electromagnet made in the shape of a horseshoe (in other words, in a U-shape). The permanent kind has become the most widely recognized symbol for magnets. It is usually depicted as red and marked with ′North' and 'South' poles. Although rendered obsolete in the 1950s by squat, cylindrical magnets made of modern materials, horseshoe magnets are still regularly shown in elementary school textbooks.
Emergency power systemAn emergency power system is an independent source of electrical power that supports important electrical systems on loss of normal power supply. A standby power system may include a standby generator, batteries and other apparatus. Emergency power systems are installed to protect life and property from the consequences of loss of primary electric power supply. It is a type of continual power system. They find uses in a wide variety of settings from homes to hospitals, scientific laboratories, data centers, telecommunication equipment and ships.
Force between magnetsMagnets exert forces and torques on each other due to the rules of electromagnetism. The forces of attraction field of magnets are due to microscopic currents of electrically charged electrons orbiting nuclei and the intrinsic magnetism of fundamental particles (such as electrons) that make up the material. Both of these are modeled quite well as tiny loops of current called magnetic dipoles that produce their own magnetic field and are affected by external magnetic fields.
Collecteur tournantvignette|upright=1.5|Principe du collecteur tournant Les collecteurs tournants ou rotatifs sont des organes électriques, présents notamment dans des moteurs, permettant de créer une connexion électrique entre une partie fixe (stator) et, une partie tournante (rotor). Ils sont utilisés dans le cas d'une rotation multi-tours du rotor autour du stator, là où une transmission par câble serait impossible (car le câble s'enroulerait autour du stator et causerait très rapidement une défaillance électro-mécanique).
