340 



AL TURN A TING CURRK\ 7 N 



the power-supply line b'b. The voltage of the battery being 

 charged is somewhat less than the voltage between line a' a and 

 line b'b. Therefore, the potential of the graphite anode is differ- 

 ent from the potential of point c, usually by approximately 5 or 6 

 volts. Consequently, during one half-cycle the potential of the 

 filament is negative with respect to that of the anode and during 

 the next half-cycle its potential is positive with respect to that 

 of the anode. 



When the filament is negative, the negative charges or electrons 

 are repelled by it, because like charges repel each other. These 



Transformer 

 2.5- Volt Tap 



Battery 

 being 

 charged U 



Rectified Current 



(a) 



FIG. 312. Tungar rectifier. 



electrons attain a considerable velocity and break up the gas 

 particles into ions. The region between the filament and the 

 anode becomes conducting and as a result current flows from a 

 into the positive terminal of the battery, through the battery 

 to the anode, to c and then to 6. 



When the filament is positive, the electrons or negative charges 

 which it tends to emit due to its incandescence are attracted 

 toward the filament, since positive and negative charges attract 

 each other. Consequently, the electrons which produce the ion- 

 izing action are withdrawn from the region between the filament 

 and the anode. As a result the gas is no longer ionized and it 

 ceases to be a conductor. No current can flow, therefore, during 

 this half-cycle. The current can flow only in one direction, 



