Uses of Electromagnets 227 



7. Compare the functions of a dynamo and an electric motor. 



8. Name several practical household uses of electric motors. 



9. Why will a thin wire become hotter than a thick wire under a heavy 

 electric current? 



10. Why do men handling electric wires often use rubber gloves? , 



11. Is it true or false that the speed of an electric motor increases with 

 the increase of current? Why? 



12. Name some advantages of transforming water power into electricity. 



13. Why are house electric wires insulated and trolley wires not 

 insulated? 



14. Suggest how you think a physician might use an electromagnet to 

 remove small pieces of metal that had become imbedded in the 

 flesh. 



15. Suggest advantages of an electromagnet over an ordinary hook and 

 chain for handling scrap iron with a crane. 



16. State the principle of the transformer. Describe a simple transformer. 

 Name two uses of a transformer. 



17. Describe the structure of a telephone transmitter. 



18. Trace the various steps in transmitting a message from speaker to 

 hearer over a telephone. 



19. Name several ways in which the telephone has affected our modern 

 life. 



20. Why are the insulated wires of a house lighting system usually carried 

 in metal tubing? 



PROJECTS 



1. Make a labeled drawing of a simple electromagnet. Then construct 

 the magnet. 



2. Make a labeled drawing of a simple electric bell. Connect up a bell and 

 study its workings. 



3. Using the electromagnet already constructed, make a model of a simple 

 electric crane. Demonstrate the lifting power of the electromagnet 

 with nails and small bits of iron. 



OUTDOOR OBSERVATION 



1. Pay a visit to an electric light plant. Then observe the outdoor dis- 

 tribution system of the current. Notice the forms of insulators in use 

 and the places where they are used. Notice how connections are made 

 between street wires and the house meter. 



2. Observe how electricity is distributed from power house to electric 

 cars. Note the character of the rail connections. Notice the method 

 of supporting the electric wires. Observe how the motorman controls 

 his motor. 



