. A text book of physics, for the use of students of science and engineering . turning moment is Hml, where I is the length of the magnet ordistance between the poles. This couple consists of two parts, thefield H and the part ml belonging to the magnet. The quantityml is called the magnetic moment M of the magnet. Hence, Couple =HM. As a rule magnets do not have the two poles situated exactly atthe ends, and hence both m and I are indefinite quantities. Still, the magnetic moment M is not indefinite, for itmay be measured by mechanical means, bydetermining the couple necessary to holdthe magn
. A text book of physics, for the use of students of science and engineering . turning moment is Hml, where I is the length of the magnet ordistance between the poles. This couple consists of two parts, thefield H and the part ml belonging to the magnet. The quantityml is called the magnetic moment M of the magnet. Hence, Couple =HM. As a rule magnets do not have the two poles situated exactly atthe ends, and hence both m and I are indefinite quantities. Still, the magnetic moment M is not indefinite, for itmay be measured by mechanical means, bydetermining the couple necessary to holdthe magnet at right angles to a given , the magnetic moment may also bedefined as the couple required to hold amagnet at right angles to a field of unit intensity. Couple acting on a magnet in any position. —If the magnet be inclined at an angle 6to the field H (Fig. 723) the force on eachpole is still Hw, but the perpendicular dis-tance between the forces isAN = I sin 6 :.. couple =V\ml sin 6= HM sin this it is seen that when 0 = 90°, the couple is HM, as found. Fig. 723.—Couple noting on a magnet inclnetie field. ned to a mag- above, and when 0 = 0° the couple is zero, since sin0°=0. Hence, 782 MAGNETISM AND ELECTRICITY CHAP. the only position in which a freely suspended magnet is in equilibriumin a given field is when its direction is coincident with that of thefield. Field due to a bar magnet.—The general form of the field dueto a bar magnet is shown in Fig. 716. The strength of field atcertain points may be calculated without difficulty. Thus, take a point P (Fig. 724) onthe line passing throughthe poles of the magnet ofpole strength m. Let Ibe half the length of themagnet and d the distanceof P from its middle the distance of Pfrom N is (d -1), and fromS the distance is (d + l). Imagine a unit N poleplaced at P. Force on unit pole due to N=73—jrs-(d - If Force on unit poledue to S =
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Keywords: ., bookcentury1900, bookdecade1910, bookpublishe, booksubjectphysics
