224 



ADVANCED ELECTRICITY AND MAGNETISM. 



effect of the wire resistance is to cause the magnetic energy in the 

 wave to decrease thus causing the wave to become impure. 



When a charged condenser is left standing a very small current 

 flows through the imperfectly insulating dielectric of the con- 

 denser and the electric energy of the condenser is slowly converted 

 into heat in the insulating material, and if we imagine that a 

 pure wave has suddenly entered upon a transmission line which 

 is not perfectly insulated, then the immediate effect of the imperfect 

 insulation is to cause the electrical energy in the wave to decrease, 

 thus causing the wave to become impure. 



Wave distortion. Imagine a pure rectangular wave pulse to 

 have entered a transmission line which has wire resistance. This 

 wave is represented in Fig. 159. After this wave has traveled a 



wire _^_^.^_^ wire 



wire 



_*. _ wire 



W 



wire 



axis of x 



Fig. 159. Fig. 160. 



Fig. 159 represents a pure rectangular wave traveling along a transmission 

 line, and Fig. 160 represents the state of affairs after an interval of time A/ has 

 elapsed. The development of a tail hi Fig. 160 is due to wire resistance. 



very short distance along the line, the magnetic energy in the 

 wave will have been reduced by the effect of wire resistance and 

 the wave will have become impure. This impure wave then 

 breaks up into two pure waves, one of which, containing nearly 

 all of the energy of the original wave, travels forwards, and the 

 other travels backwards. This action is here described as taking 

 place after the original wave has traveled a very short distance 

 along the line, but in fact the action is continuous ; the rectangular 

 wave sends out backwards a long drawn out ribbon wave thus 



