406 



GENERAL SCIENCE 



18. What is the difference between the resistance offered by 

 Tungsten lights and carbon lights? 



19. Why does great resistance reduce the cost of operation? 



20. Why is the electrolytic method of cleaning silver better than 

 the polishing method? 



USES OF MAGNETS AND CELLS 



Electric Bell. 



Examine the electric bell. 



What are the magnets H and / called? 



G N is a piece of soft iron. 



Why is GN pulled to the magnets H and / when a current of 



FIG. 305. 



electricity enters the wire around the magnets? The current enters 

 the bell at A and leaves at B. Why does the hammer F hit the 

 bell when the current is turned on? What happens at D and E 

 when G N is pulled toward the magnet? When the current is broken, 

 what happens to the magnets H and /? 



As soon as 7 and H lose their magnetism, GN springs back, 

 causing D and E to meet again. 



Why do G and H become magnets again? 



How quickly do you think G and H become magnets, and lose 

 their magnetism? 



What is the push button for? 



