ELEMK.V1 ARY LAWS OF CONTINUOUS CURRENTS 3 



electric current will flow through the wire. The current 

 may he detected by any one of its actions as described in 

 section 1. The question arises as to what action causes 

 the current to flow through the wire. The wire by itself 

 cannot produce a current, so it is evident that there must 

 be some action in the vessel contai:. 111,12; the- two plates and 

 sulphuric arid (Vailed a primary cell) which action results 

 in a current when the two plates are connected together 

 outside the solution. Such a cell, which, by some internal 

 action, is able to produce and maintain an electric current 

 is said to generate an electromotive force. 



It must be remembered that, if current is to be pro- 

 duced by the cell, the two terminals of the cell must be 

 connected by some conducting body, i.e., some body through 

 which an electric current passes freely. But such a cell 

 generates an electromotive force (generally abbreviated to 

 e.m.f.) whether its terminals are connected together or not. 

 Some action takes place between the solution and the two 

 metal plates of the cell and this action causes one plate to 

 be at a higher electric pressure than the other. If two 

 conducting bodies, between which there exists a difference 1 

 of electric pressure, are connected together, current will 

 flow from the point of higher pressure to that of lower 

 pre^ure. The current is said to be caused by the e.m.f. 

 of the cell but, Bfl stated before, the cell generates an e.m.f. 

 whether current Hows or not. 



Generation of e.m.f. by Candm-tor* Cutting a Magnetic 

 r'n'ld. A machine consisting chiefly of a set of conductors 

 revolving in a magnet ir field fan electric generator) has, 

 when the conductors are thus made to move, some internal 

 action which causes its two terminals to be so charged that 

 there is between them a difference of electric pressure. 

 If the terminals of the machine are connected by a wire, 

 current will flow from one terminal to the other through 

 the connecting wire, and this flow will continue as long as 

 the connecting wire is left in place. 



