220 



VARIABLE STATE. 



This strength is a function of the time; it is zero for /=0, and 



<)I i 



becomes a maximum when = 0, which gives z 2 = - . If T is the 



ot 2 



time of the maximum we have 



*JK* 



2. 2 



The curve A (Fig. 57) represents the value of the expression 

 \ -e~~ t which is proportional to the strength of the current. The 



Fig. 57- 



time of the maximum being proportional to a 2 ,* 2 , we see that the 

 curve is the more bent, the greater is the distance x from the point 

 taken as the origin. 



229. MOMENTARY CONTACTS. Let us suppose that the end 

 of the wire is only put in momentary -contact with a source at 

 constant potential, that is to say, that this end is only raised to 

 potential V for a very brief period T, and is then connected with the 

 earth. 



The potential at any given point will be obtained by superposing 



