ELECTRIC OSCILLATIONS AND ELECTRIC WAVES. 267 



21. A wave disturbance from a lightning stroke travels along 

 the single-wire line of problem 20. Find the resistance of a 

 lightning arrester ground connection which, if placed at the end 

 of the line, would absorb the wave disturbance completely and 

 reflect not at all. Ans. 511 ohms. 



22. The value of the short-circuit current in Fig. 158 is, say, 

 100 amperes and the value of I/ L/C for the line is, say, 100 

 "ohms." The inductance of the generator is assumed to be 

 indefinitely large so that line current at the generator retains its 

 value of 100 amperes for a fairly long time after the short- 

 circuited line is snapped open at the distant end. The line is 

 1 86 miles long. Plot a curve showing the voltage across the 

 middle of the line as a function of elapsed time, neglecting 

 effects of line resistance and leakage, and assuming the insulation 

 strength of the line to be indefinitely great. 



23. The line of problem 20 is 93 miles long and open at both 

 ends, and it is uniformly charged (one wire positively and the 

 other wire negatively) so that the voltage across the line is every- 

 where 10,000 volts and the current in the line is everywhere zero. 

 One end of the line is suddenly closed with a switch of negligible 

 resistance. Plot curves showing voltage and current at the 

 middle of the line as functions of elapsed time. 



24. Two oppositely moving rectangular waves A and B 

 each two miles long come into superposition. The voltage in 

 A is + 5,000 volts and the voltage in B is + 2,500 volts, and 

 the value of V L/C for the line is 100 "ohms'." What is the 

 total voltage and total current in the two miles of line where the 

 two waves come into exact superposition? Ans. + 7,500 volts 

 and +25 amperes. 



25. Imagine a two-mile section of the line of problem 24 to 

 have + 10,000 volts across it everywhere and 50 amperes in 

 it everywhere. What is the state of affairs on the line / seconds 

 later, where / is the time for an electric wave to travel three 

 miles? Ans. A section of the line two miles long in each 



