Magnets and Electric Currents; An Elementary Treatise for the Use of Electrical Artisans and Science Teachers (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1902 edition. Excerpt: ...a lagging behind or want of correspondence between two things. The firm line curve in Fig. 49 delineates the relation of magnetic flux density to magnetic force during these operations. It will be seen that, after the magnetic force has been applied and removed, magnetic flux still lingers in the iron or is retained, and this property of the iron is called its Retentivity. The ordinate O Q represents the magnetic flux density remaining after the force has been again reduced to zero. The ordinate O P represents the maximum value of the flux density attained, and the ratio of O Q to O P (expressed as a Fig. 49.--Portion of Magnetisation Curve of Irua Ring showing Hysteresis. percentage) is the measure of the retentivity of the iron under those conditions. It may even reach 90 per cent. In the next place, after reducing the magnetising force to zero let us suppose it is reversed, and a force of--I applied, and then--2, and so up to--4; after which, let the force be again increased and brought back to zero. In this way a complete cycle of magnetising force is applied, ranging from 0 to + 4, from +4 to 0, from 0 to--4, and from--4 back to 0 again. Corresponding to this, we find that the magnetic flux in the iron goes through a cycle or range of periodic values, and that the flux and force are related to one another, as shown by the ordinates and abscissae of the closed curve in Fig. 50. This curve is called a hysteresis diagram or loop. The ordinate O P, represents the maximum value of the magnetic flux density during the cycle. The ordinate O Q represents the magnetic flux density retained in the iron after the force is withdrawn, and represents, therefore, the retentivity of the iron. The inter Fig. 50. teresis Loop for Iron Ring. Complete Hys-cept...