10.The Age of Electronic Materials 179 FIGURE 10.2.(a)Oersted's ex- periment in which a com- pass needle is deflected by a wire conveying an electrical current (a sophisticated ver- sion of this design served later as a galvanometer).(b) Schematic representation of Faraday's device in which a current-carrying wire rotates around a permanent mag- net.Note that the trough is filled with liquid mercury to (a (b) provide an electrical contact. Ampere discovered that two parallel wires through which currents flowed in the same directions attracted each other,whereas they were repelled when the currents flowed in opposite directions.) Faraday's second and probably greatest single discovery was born out of his conviction that,if electric currents would produce magnetism,the reverse must also occur.Experiments with sta- tionary magnets and wires failed.Today we realize that this must be the case;otherwise,a perpetual motion would be created.Fi- nally,in 1831,Faraday demonstrated electromagnetic induction in a series of fundamental experiments.The first of them involved an iron ring on which two separate coils were wound as shown in Figure 10.3(a).If the current in the primary circuit was opened and closed,a galvanometer connected to the secondary winding deflected momentarily each time (and in opposite directions,re- spectively).In a second experiment,Faraday moved a permanent magnet in and out of a wire coil to which a galvanometer was con- nected.He found deflections in opposite directions depending on which way the magnet was moved;Figure 10.3(b).Finally,a wire or coil that was moved within the field of a horseshoe magnet showed,likewise,deflections on a galvanometer,Figure 10.3(c). Based on these experiments,Faraday created the first dynamo ma- chine consisting of a copper disk which he rotated between the poles of a large permanent magnet.He tapped the induced cur- rent from the axis and the edge of that disk. The common element of these experiments was eventually rec- ognized to be that any change in magnetic flux induces a pulse of an electrical current in a loop-shaped piece of wire.Moreover,Fara-Ampère discovered that two parallel wires through which currents flowed in the same directions attracted each other, whereas they were repelled when the currents flowed in opposite directions.) Faraday’s second and probably greatest single discovery was born out of his conviction that, if electric currents would produce magnetism, the reverse must also occur. Experiments with sta￾tionary magnets and wires failed. Today we realize that this must be the case; otherwise, a perpetual motion would be created. Fi￾nally, in 1831, Faraday demonstrated electromagnetic induction in a series of fundamental experiments. The first of them involved an iron ring on which two separate coils were wound as shown in Figure 10.3(a). If the current in the primary circuit was opened and closed, a galvanometer connected to the secondary winding deflected momentarily each time (and in opposite directions, re￾spectively). In a second experiment, Faraday moved a permanent magnet in and out of a wire coil to which a galvanometer was con￾nected. He found deflections in opposite directions depending on which way the magnet was moved; Figure 10.3(b). Finally, a wire or coil that was moved within the field of a horseshoe magnet showed, likewise, deflections on a galvanometer; Figure 10.3(c). Based on these experiments, Faraday created the first dynamo ma￾chine consisting of a copper disk which he rotated between the poles of a large permanent magnet. He tapped the induced cur￾rent from the axis and the edge of that disk. The common element of these experiments was eventually rec￾ognized to be that any change in magnetic flux induces a pulse of an electrical current in a loop-shaped piece of wire. Moreover, Fara- 10 • The Age of Electronic Materials 179 FIGURE 10.2. (a) Oersted’s ex￾periment in which a com￾pass needle is deflected by a wire conveying an electrical current (a sophisticated ver￾sion of this design served later as a galvanometer). (b) Schematic representation of Faraday’s device in which a current-carrying wire rotates around a permanent mag￾net. Note that the trough is filled with liquid mercury to (a) (b) provide an electrical contact. – – + + N S Hg