CHAPTER V 

 MAGNETISM AND MAGNETIC CIRCUITS 



1. Upon cross-section or coordinate paper construct the mag- 

 netization curves from page 105, for cast iron, cast steel, wrought 

 iron and sheet steel. Plot with magnetizing force H for abs< 

 and density B for ordinates. Use the same scale for all the curves 

 and, while taking one that is easily read, choose it so as to occupy 

 with the curves as much of the sheet as practicable. Carry the 

 curves to about H = 200. (30 min.) 



2. Given a ring of cast iron, 50 cm. in circumference; required 

 the gilberts necessary to give 6500 gausses, and also the turns, 

 if the current is 5 amperes. (2 min.) 



3. If a cut be made in the ring of the last problem and spread 

 out to i cm. gap, what will be the total number of turns necessary 

 for the same density? (2 min.) 



4. A forged ring has a mean 1 diameter of 45 centimeters, and an 

 area of 30 sq. cm. The flux is 450 kilomaxwells. Required the 

 gilberts and the ampere turns necessary. (5 min.) 



5. Required the reluctance in oersteds of the above ring at the 

 density used; also the permeability. (4 min.) 



6. Required the reluctance in cersteds of a cast-iron ring of the 

 same dimensions as in problem 5 and having a permeability of 

 200. What density does this indicate? Compare with the reluct- 

 ance found in problem 5. (8 min.) 



7. A horseshoe-shaped magnet for hoisting rails is forged of 

 wrought iron and has a magnetic path 40 cm. long; the oxide 

 on the rail is 0.1 mm. thick (note the two gaps), and the p:ith 

 through the rail is 15 cm. The density in the magnet is 16,000 

 gausses, and the cross-section of the rail is double that of the mag- 

 net. Magnetizing force H for both irons is to be taken as for 

 wrought iron. Required the number of turns necessary in the 

 winding if the exciting current is two amperes. (4 min.) 



8. A cast-steel magnetic clutch for driving a pulley must pull 

 its armature up when it is 1 mm. away (note the two gaps). Its 



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