ELECTROMAGNETS. MAGNETISM OF IRON. IOI 



The distance across the air gap is 3/8 inch. Find the magneto- 

 motive force across the air gap in gilberts and in ampere- turns. 

 Ans. 3,333-5 gilberts or 2,650 ampere-turns. 



2. Find the magnetomotive force in gilberts and in ampere- 

 turns along a vertical line 10 meters long at a place where the 

 intensity of the earth's magnetic field is 0.56 gauss and its dip 

 is 72. Ans. 533 gilberts or 424 ampere-turns. 



3. A slim rod 25 centimeters long is made into a link which 

 passes through a coil of 50 turns of wire in which a current of 

 15 amperes is flowing. Find the average value along the rod 

 of the component parallel to the rod of the magnetic field due 

 to the coil. Express the result in gausses. Ans. 37.7 gausses. 



4. An iron ring is wound with 1,000 turns of wire, and the wire 

 has a current of 2 amperes flowing in it. The ring has an air 

 gap in it and the distance across the gap space is 0.75 centimeter. 

 Find the magnetic field intensity in the gap space assuming that 

 the magnetomotive force of the winding is all concentrated on 

 the gap space. Ans. 3,350 gausses. 



5. An iron rod 2 centimeters square and 20 centimeters long 

 is magnetized to an intensity of 1,000 units pole per square 

 centimeter section when it is placed in a region which, but for 

 the action of the poles of the rod, would be a uniform field parallel 

 to the rod and of an intensity of 102 gausses. Assuming the 

 poles of the rod to be concentrated at its ends, calculate the net 

 magnetizing field at the center of the rod. Ans. 22 gausses. 



6. Find the total magnetic flux through the middle part of the 

 rod specified in problem 5. Ans. 50,353.6 maxwells or lines. 



Note. One part of the flux is 4r m and the other part is <%, where &C is the 

 net magnetizing field at the middle of the rod and 5 is the sectional area of the 

 rod. 



7. A bar magnet of hard steel is 2 centimeters square and 20 

 centimeters long, and the strength of each pole of the magnet is 

 2,000 units. The magnet is placed in a region which, but for 

 the presence of the magnet, would not be a magnetic field. 



