. The Ontario high school physics. directionas to produce a continuouscurrent in the whole series,which will fl(jw from onecollecting ring to is evident, also, that tlie FiQ. 539.—A self-excitinff alternating current dy- rlii-(»f>fir>n r\f fliia /^nvT-onfnamo, driven by the pulley P. There are four -^♦-^Lauu Ui tlUb CUlieno f!-Atte :n;atu;e:^rthists;^ h S; ^vlU be reversed the instant consists of two armatures wound together. One fl,„ fialrl anrl QT-mofnTO r»r>ila is joined to a commutator rf, on which rest four ^^^*^ ^^^^^^ ^^ «* mature COHS brushes 6, b, b (one not see
. The Ontario high school physics. directionas to produce a continuouscurrent in the whole series,which will fl(jw from onecollecting ring to is evident, also, that tlie FiQ. 539.—A self-excitinff alternating current dy- rlii-(»f>fir>n r\f fliia /^nvT-onfnamo, driven by the pulley P. There are four -^♦-^Lauu Ui tlUb CUlieno f!-Atte :n;atu;e:^rthists;^ h S; ^vlU be reversed the instant consists of two armatures wound together. One fl,„ fialrl anrl QT-mofnTO r»r>ila is joined to a commutator rf, on which rest four ^^^*^ ^^^^^^ ^^ «* mature COHS brushes 6, b, b (one not seen). This generates a ^.^.^.^ panTi nflipr direct current (see next section) which is used to -g^m -iciuc Cctcii the field-magnets. The other armature is £~^. ., , p i, joined to the three collecting rings c, c, c, from OlUCe the number Ot altcr- which the three-phase alternating current is led off. p ,i • , o nations or tins current toreach revolution of the armature ec^uals the number of poles in. 446 INDUCED CURRENTS the lield-magnet, the numl)er of alternations per minute isequal to the number of poles in the field-magnet multipliedby the number of revolutions made by the armature perminute. 528. Production of a Direct Current—The Commutator. When an electric current flows continuously in one directionit is said to be a direct current. The current in an armaturecoil changes direction, as we have seen, at regular periods. Toproduce a direct current with a dynamo it is necessary toprovide a device for commuting the alternating into a directcurrent. This is done by means of a coininiitator. It con-sists of a collecting ring made of segments called comTYiuiatorplates, or bars, insulated from one another. The terminals ofthe coils are connected in order with the successive plates ofthe ring. Take, for example, the case of a single coilrevolved in a bipolar field, as considered in (§ 524). The commutator consists of twoa semi-circular plates, (Fig
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