264 ADVANCED ELECTRICITY AND MAGNETISM. 



3. The tension of a string is 25 million dynes and each centi- 

 meter of the string has a mass of 0.2 gram. What is the velocity 

 of a wave or bend on the string? Ans. 11,280 centimeters per 

 second. 



4. A transmission line consists of two copper wires each 0.5 

 inch in diameter and the wires are 24 inches apart center to 

 center, (a) What is the inductance of the line per mile of the 

 double line? (b) What is the capacity of the line per mile of 

 double line? (c) What is the velocity of wave propagation on 

 the line? Ans. (a) 0.00294 henry per mile; (b) 9.798 X IO" 9 

 farads per mile; (c) 186,000 miles per second. 



5. A 10,000 volt generator of negligible resistance and induct- 

 ance is switched on to the end of the line of problem 4. What is 

 the voltage and current in the ribbon wave which shoots out 

 along the line? Ans. 10,000 volts, 1.835 amperes. 



6. A battery of which the resistance is i ,500 ohms and of which 

 the electromotive force is 10,000 volts is switched on to one end 

 of the line of problem 4. What is the voltage and current in the 

 ribbon wave which shoots out along the line? Ans. 7,852 volts 

 and 1.433 amperes. 



Note. Let E be the required voltage and I the required current. Then 

 Ell = VZ/C and E + RI = 10,000 volts, where R is the resistance of the 

 battery. 



7. The line in problem 5 is 18.6 miles long and it is open at 

 the distant end. The 10,000 volt generator is switched on to the 

 line and disconnected after 0.00015 second. What is the current 

 and voltage distribution over the line at the instant when the 

 generator is disconnected? Ans. Over the half of the line next 

 the generator the voltage is everywhere 10,000 volts and the 

 current is everywhere 1.835 amperes; over the distant half of 

 the line the voltage is 20,000 volts and the current is zero. 



8. The distant end of the 18.6 mile line in problem 5 is short- 

 circuited and the 10,000 volt generator is disconnected (leaving 

 the generator end of the line open) o.oooi second after it was 



