ELECTROMAGNETS. MAGNETISM OF IRON. 103 



12. (a) Find the work in ergs spent in magnetizing a wrought 

 iron bar 3 inches square and 20 inches long from a neutral condi- 

 tion to cB 16,000 lines per square centimeter, using the 

 tabular values of c& and 3f given in Art. 56. (b) Find the work 

 in ergs required to magnetize a cast-iron rod of the same size from 

 a neutral condition to $ = 9,000 lines per square centimeter. 

 Ans. (a) 32.6 X io 6 ergs. (6) 33.9 X io 6 ergs. 



Note. Plot the c& and &C curves from the tabular values given in Art. 56. 

 Divide the areas between the curves and the <B axis into a number of narrow 

 strips, and calculate the area of each strip. Add these areas to get the total area. 



13. A transformer core contains 96 cubic inches of the best 

 quality of transformer iron. The core is carried through 133 

 magnetic cycles per second between the limits cB = 3,500 

 gausses, by means of an alternating current. Find the hysteresis 

 loss in the core in watts. Ans. 14.7 watts. 



