SOME WAYS OF PRODUCING ELECTRICITY 181 



1. There are only a few metals that can be magnetized or that 

 can be attracted by a magnet. 



2. Electric charges can be given to bodies of matter. Non- 

 conducting bodies hold these charges for a time. 



3. Electricity is believed to consist of negative particles called 

 electrons and positive particles called protons. 



4. Electrical energy is produced only at the expense of some 

 other kind of energy. 



Before making your review summary, test your knowledge of 

 the facts of the unit by checking over the text so as to be sure you 

 know the facts underlying the generalizations. Then, using the 

 generalizations, the material in the text, and everything you have 

 read, seen, or done yourself, make a summary outline for your 

 notebook. This outline you may use when you make a recitation. 



TEST ON FUNDAMENTAL CONCEPTS 



Make two vertical columns in your workbook. Head one CORRECT and 

 the other INCORRECT. Under the first place the numbers of all statements 

 you believe to be correct. Under the second place all the numbers of the 

 statements you believe to be incorrect. Your grade = right answers X 5. 



I. When glass is rubbed with silk : (1) the silk takes a negative 

 charge and the glass a positive charge ; (2) the glass is electrified 

 but not the silk ; (3) the amount of electricity produced is the same 

 in both bodies ; (4) the glass and silk will repel each other. 



II. Electricity may be produced by : (5) friction between paper 

 and cloth ; (6) putting rods of aluminum and iron into a salt solu- 

 tion and letting the outside ends touch each other ; (7) chemical 

 action in a storage battery ; (8) an electric motor. 



III. Every magnet has: (9) two poles which attract iron; 

 (10) two unlike poles; (11) a magnetic field; (12) an electric 

 current surrounding it. 



IV. A dry cell : (13) produces electricity from chemical energy; 

 (14) contains no water ; (15) has two poles, north and south ; 

 (16) produces no current on a closed circuit. 



V. The needle of a magnetic compass: (17) is a temporary 

 magnet ; (18) points to the earth's geographic north pole ; (19) takes 

 the direction of the earth's lines of magnetic force ; (20) always 

 points in an east to west direction. 



THOUGHT QUESTIONS 



1. What are some objections to the use of the magnetic compass 

 to direct the course of a ship? 



