MAGNETS AND ELECTROMAGNETS 



247 



William Thompson 



FIG. 387. MICHAEL FARADAY 



in a coil about a soft piece 

 of iron, the coil and iron 

 would act like a magnet 

 when the current was flow- 

 ing but would lose their 

 magnetism when it was 

 turned off. Figures 387 and 

 388 show Faraday and his 

 first electromagnet. 



An electromagnet has 

 poles exactly like a bar 

 magnet. These poles de- 

 pend upon the direction in 

 which the current is flow,- 

 ing about the soil. That is, 

 if the current is made to flow through a coil in the 

 opposite direction, the poles of the electromagnet will 

 also be reversed. 



The strength of an electromagnet can be changed 



either by changing the 

 number of turns of wire 

 or by changing the 

 amount of current which 

 is flowing through the 

 coil. 



Electromagnets have 

 many uses. Because an 

 electromagnet can be 

 made to lose its magnet- 



ism by turning off the 



~ frag^y," 1 . mi 



W^Sjj&StjISilJ^mi current, it is useful for 



fiS^!5?lM ik loading and unloading 



iron around steel mills. 

 When a large magnet 

 like the one shown in 

 Figure 389 is swung on 

 a crane over a carload of 

 scrap iron, pig iron, or 

 railroad rails, and cur- 

 rent is turned on, the ma- 

 terials can be lifted out and carried by the crane to the 

 place where they are to be stored to await further use. 

 The materials are released from the magnet when a 

 switch is opened and the current is turned off. 



Other uses for the electromagnet are found in the 

 telephone receiver, the telegraph sounder, the electric 

 bell, the electric motor, and the generator. 



REFERENCES FOR FURTHER STUDY 

 Texts 



Caldwell and Curtis, Science for Today, Chaps. 21 and 22 

 Clement, Collister, and Thurston, Our Surroundings, Chaps. 



14 and 16 



Hunter and Whitman, My Own Science Problems, Unit 7; 

 Science in Our World of Progress, Unit 7 ; Science in Our 

 Social Life, Unit 7 



FIG. 388. FARADAY'S FIRST 

 ELECTROMAGNET 



Lake, Harlcy and Welton, ExpMrfflfthe World of Science, 

 Chap. 23 



Pieper and Beauchamp, Everyday Problems in Science, Unit 

 14 



Powers, Ncuner, and Bruner, Man's Control of His Environ- 

 ment, Unit V 



Skilling, Tours through the World of Science, Tour 10 



Van Buskirk and Smith, The Science of Everyday Life, Chap. 

 17 



Watkins and Bedell, General Science for Today, Chap. 24 



Webb and Beauchamp, Science by Observation and Experi- 

 ment, Unit 5 (part) 



Wood and Carpenter, Our Environment: How We Use and 

 Control It, Topic 9 



Special references 



Lunt, Everyday Electricity 

 Meister, Magnetism and Electricity 

 Morgan. The Boy Electrician 



Courtesy Ohio Electric Manufacturing Company 



FIG. 389. A LARGE ELECTROMAGNET 



WHAT YOU SHOULD AIM TO ACQUIRE FROM 

 THIS STUDY 



1. What the different kinds of magnets are and how 

 they work. 



2. What a compass is and why it points north and 

 south. 



3. What a magnetic field is and how it may be 

 mapped. 



4. What magnetic lines of force are and what are 

 their properties. 



5. What an electromagnet is, its properties, and what 

 it is used for. 



TEST OF MASTERY OF TOPIC 



In your notebook complete the statements, answer the 

 questions, and comply with the instructions. 



1. Every magnet has poles. 



2. Like magnetic poles and unlike poles 



3. The north pole of a compass needle points 



4. The earth is a large with its north pole in the 



hemisphere and its pole in the hemisphere. 



5. Make a diagram of a bar magnet and draw the lines 

 of force as they should appear about it. 



6. is used to map the magnetic field about a magnet. 



7. The field about a magnet is made up of 



8. and were two men interested in the early 



development of the electromagnet. 



