. Dental electro-therapeutics. th pole; if it is balanced on a pivot in thecentre, which is the equator or neutral zone of the magnet,the north pole will swing to the north as any ordinarypocket compass does. From the ends of the magnet themagnetic force radiates in curves in the direction fromone pole to the other, there being a considerable spaceabout the magnet which is the magnetic field. The strengthof the force in a bar magnet is greater at each end. Ina curved magnet, on the other hand, the greatest force isexerted between the two poles from their nearest points. This magnetic force whi
. Dental electro-therapeutics. th pole; if it is balanced on a pivot in thecentre, which is the equator or neutral zone of the magnet,the north pole will swing to the north as any ordinarypocket compass does. From the ends of the magnet themagnetic force radiates in curves in the direction fromone pole to the other, there being a considerable spaceabout the magnet which is the magnetic field. The strengthof the force in a bar magnet is greater at each end. Ina curved magnet, on the other hand, the greatest force isexerted between the two poles from their nearest points. This magnetic force which permeates the field aboutthe magnet is conducted by the air, but air has been found 76 ELECTRO-PHYSICS to be a poor conductor of magnetism, whereas iron is a goodconductor and if the magnet is strong enough iron broughtin contact with it will itself become magnetized to somedegree. Fig. 17 s V\\ ? /-•; :>:J^:§;;:> - \ V N < axis - ?--;? 11 w. s Lines of force of magnetic field. Fig. 18. Electro-magnet. A temporary magnet is made by winding insulatedcopper wire around an ordinary piece of soft iron bentin the shape of a horseshoe and by passing an electriccurrent through the wire. As the wire does not touch theiron it is evident that the magnetism which is impartedto the iron is obtained from a magnetic field about thecurrent conducting wire. This magnetic field exists aroundall wire conducting electric current and the force of thefield is intensified by the curving of the wire (making a MAGNETIC FIELD 77 spiral of it, as by winding stiff copper wire around a leadpencil and removing the pencil), and also by the intensityof the current passed through the wire; the field is alsostronger when the iron is placed in it. A magnet made by passing current through wire en-circling a piece of soft iron is only magnetic so long as thecurrent is passing, it is a temporary magnet. Sir Oliver Lodge points out that the magnetic fieldabout a current conducting wire exe
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