234 



ADVANCED ELECTRICITY AND MAGNETISM. 



obtained with the help of Fig. 171 in which AB is a wooden 

 cylinder with equidistant radial rods (arrows) set into it in a 

 straight row, that is, all lying in one plane ; the wooden cylinder 

 with its attached arrows is supposed to be rotating at a speed of 



Fig. 171. 



/ revolutions ( = 2irf radians) per second in a counter-clockwise 

 direction as seen from the end B\ and the projections of the 

 attached arrows upon the plane of the paper represent the up 

 and down movements of the various particles of the vibrating 

 string. 



When a simple train of electromagnetic waves, like Fig. 144, 

 travels over a transmission line and is reflected or turned back 

 at the end of the line, the superposition of the original and 

 reflected wave trains constitutes what is called a simple standing 



short-circuited 

 end 



/A-//;; 4 





axis of 

 rotation 



D 



C B A 



Fig. 172. 

 Clock diagram model of a standing wave train. 



e2 ^direction of clock-diagram 

 rotation 



wave train or a simple mode of oscillation of the transmission line. 

 A clear idea of voltage and current distribution over such an 

 oscillating transmission line may be obtained with the help of 

 Fig. 172. This figure represents two sets of equidistant radial 



