74 ADVANCED ELECTRICITY AND MAGNETISM. 



1,500,000 lines of force are produced through the field core. 

 Assuming that the flux is proportional to the exciting current, 

 find the inductance of the field coil in henrys. Ans. 75 henrys. 



19. A battery having an electromotive force of 10 volts and a 

 resistance of one ohm is connected to a coil of wire wound on an 

 iron core. The coil has 1,000 turns of wire and its resistance is 

 4 ohms. What is the current in the coil when the magnetic 

 flux in the core is increasing at a rate of 500,000 lines per second? 

 Ans. I ampere. 



20. A certain spool wound full of wire o.i centimeter in 

 diameter has an inductance of 0.08 henry. The same spool is 

 wound full of wire 0.32 centimeter in diameter? What is its 

 inductance? Ans. 0.000762 henry. 



21. A spool 5 times as large as the spool mentioned in problem 

 20 but similar in shape, is wound with wire 6 millimeters in diam- 

 eter. What is its inductance? Ans. 0.193 henry. 



22. A transmission line consists of two No. I B. & S. wires at 

 a distance of 2 feet apart center to center. Find the inductance 

 in henrys of ten miles of this line. Ans. 0.0329 henry. 



