![]() Throughout, we use blue for the North pole and red for the South. To be that acting to align the central magnet. In the sketchĪt right, the electromagnet formed by the coil of the rotor is representedĪs a permanent magnet, and the same torque (North attracts South) is seen The coil can also be considered as a magnetic dipole, or a little electromagnet,Īs indicated by the arrow SN: curl the fingers of your right hand in theĭirection of the current, and your thumb is the North pole. ![]() That is the origin of the diagram shown here. For students who know vector multiplication, it is easy to use the Lorentz force directly: F = q v X B, whence F = i dL X B. * A number of different nmemonics are used to remember the direction of the force. The other two sides of the coil act along the same line and so exert no torque.) The two forces shown here are equal and opposite,īut they are displaced vertically, so they exert a torque. The force F on a wire of length L carrying a current i in a magnetic fieldī is iLB times the sine of the angle between B and i, which would be 90° if On the current-carrying wires create a torque on the coil. The coil lies in a steady magnetic field. TheĬurrent in the coil is supplied via two brushes that make moving contact withĪ split ring. Real electric motors work, by Prof John Storey.Ī simple DC motor has a coil of wire that can rotate in a magnetic field. More complex and subtle cases described in How Of the various types of motors, you may want to go straight to the If you already understand the basic principles Real motors use the same principles, but their geometry is ![]() The schematics shown here are idealised, to make the principles obvious.įor example, the animation at right has just one loop of wire, no bearings and a very simple
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