180 HOW WE PRODUCE ELECTRICITY 



sealing wax and wool will produce two unlike charges of (5) 



The nucleus of every atom of matter contains positive particles 



called (6) Around this (7) revolve. When glass is 



rubbed with silk, (8) go from the glass to the silk, making the 



glass (9) because of the excess of (10) in it and the silk 



(11) because of the excess of (12) in it. Electrons (13) 



electrons and protons (14) protons, but protons (15) elec- 

 trons. Current electricity is merely a flow of (16) along a 



(17) (18) are materials which do not allow electricity 



to pass readily. In electric cells, electricity results from an 



expenditure of (19) energy. The common dry cell has two 



plates, zinc and carbon, and the active chemical (20) chloride. 



STORY TEST 



WENDELL EXPERIMENTS AT HOME 

 Read carefully and critically. List all the errors and suggest corrections. 



I know that friction produces heat, but I have been puzzled to 

 know why it is only in cold weather that I can get enough heat 

 by rubbing the fur on my cat's back to make sparks of fire. Last 

 night I rubbed a comb with flannel and the comb received elec- 

 trons from the flannel. I touched small bits of paper with the 

 comb. They clung to it at first but soon jumped off. Since they 

 were attracted at first I think they must have had a positive charge, 

 and when they jumped off we know they were positive because 

 they were repelled. A positive charge is easily produced by 

 rubbing glass with silk. The protons go into the glass, making it 

 positive. This morning I got a dry cell at the store. I connected 

 it through a button with wire to an electric bell. In connecting 

 to the battery I was careful to have the string or cloth covering 

 of the wire kept in place when I screwed the nuts over the wire on 

 the binding posts because if the bare wire touched them it would 

 make a short circuit and ruin the battery. When I pressed the 

 button the bell did not ring. This shows that the battery was old. 

 I shall take it back to the store and exchange it for a fresh battery. 



THE REVIEW SUMMARY 



In this unit we have only begun to find out some of the fact? 

 about electricity, therefore you will not be able to give all the 

 generalizations that you would give later on. See if you can add 

 any to the ones that follow : 



