174Fundamental Electrical and Electronic Principlesthe values of these individual eddy currents are added together, it will be found to be less than that for the solid core. The hysteresis loss is proportional to the frequency f of the a.c. supply. The eddy current loss is proportional to f2 . Thus, at higher frequencies (e.g. radio frequencies), the eddy current loss is predominant. Under these conditions, the use of laminations is not adequate, and the eddy current loss can be unacceptably high. For this type of application, iron dust cores or ferrite cores are used. With this type of material, the eddy currents are conﬁ ned to individual ‘ grains ’ , so the eddy current loss is considerably reduced. 5.16 Self and Mutual Inductance The effects of self and mutual inductance can be demonstrated by another simple experiment. Consider two coils, as shown in Fig. 5.38 . Coil 1 can be connected to a battery via a switch. Coil 2 is placed close to coil 1, but is not electrically connected to it. Coil 2 has a galvo connected to its terminals. Ecoil 1coil 2 Fig. 5.38 Fig. 5.37 When the switch is closed, the current in coil 1 will rapidly increase from zero to some steady value. Hence, the ﬂ ux produced bycoil 1 will also increase from zero to a steady value. This changing ﬂ ux links with the turns of coil 2, and therefore induces an emf into it. This will be indicated by a momentary deﬂ ection of the galvo pointer.