450 ELEMENTS OF ELECTRICAL ENGINEERING. 



space is 3,000 gausses. The armature is covered with straight 

 wires parallel to its axis. Each of these wires carries 75 am- 

 peres. Calculate the side push on each wire in dynes and in 

 pounds. Ans. 675,000 dynes or 1.518 pounds. 



13. A horizontal wire 10 meters long, stretched due magnetic 

 east and west, and carrying a current, is pushed upwards by the 

 horizontal component of the earth's magnetic field with a force 

 of 3,000 dynes. What is the direction and strength of the cur- 

 rent in the wire, the horizontal component of the earth's field 

 being 0.2 gauss? Ans. 150 amperes flowing towards the east. 



14. A horizontal electric light wire, stretched due magnetic 

 north and south, carries a current of 1,000 amperes flowing 

 towards the north. The wire is 250 meters long, the intensity 

 of the earth's magnetic field is 0.58 gauss, and the magnetic dip 

 is 63. Find the value of the force with which the earth's mag- 

 netic field pushes on the wire and specify its direction. Ans. 

 2.906 pounds, pushing towards the west. 



15. A circular coil of wire of 20 cm. radius has 1 5 turns of 

 wire. How much current is required in the coil to give a mag- 

 netic field intensity of one gauss at the center of the coil ? Ans. 

 2.122 amperes. 



16. A circular coil of wire of 20 cm. radius has 1 5 turns of 

 wire and it carries 20 amperes. Calculate the magnetic field in- 

 tensity : (a) at the center of the coil, (&) at a point in the axis of 

 the coil and distant 100 cm. from the plane of the coil, and (r) 

 at a point in the axis of the coil and distant 200 cm. from the 

 plane of the coil. Ans. (a) 9.42; (b] 0.07109; (c) 0.00929 

 gauss. 



17. A solenoid five feet long has 1,600 turns of wire, calcu- 

 late the magnetic field intensity inside of the solenoid due to a 

 current of 10 amperes in the wire. Ans. 131.8 gausses. 



18. A long iron rod two inches in diameter has one of its ends 

 projecting into the solenoid specified in problem 17. Assuming 

 that the rod is magnetized to an intensity of 1,500 units pole per 

 square cm. section, calculate the force tending to draw the rod 



