UNIT XL ELECTRICITY AND HOW WE USE IT 



"Snap!" the switch is pushed and the room is 

 flooded with light, the electric iron begins to heat, 

 the motor whirs as it gains speed to turn the washer, 

 sewing machine, or grinder. We step on the street 

 car and in a little time we are whisked from one side 

 of the city to the other. A few clicks of the telegraph 

 and a message is sent with tremendous speed to the 

 remotest corners of the globe. The receiver is taken 

 from the hook and in a few moments one may be talk- 

 ing to Seattle, New York, or Galveston. A few care- 

 ful manipulations of the dials of your radio and you 

 hear the music of New York, Los Angeles, or Havana. 

 What a wonderful thing electricity is and how de- 

 pendent we are upon it for modern convenience and 

 comfort! 



Electricity has been known since the time of the 

 Greeks, twenty-five hundred years ago. They ob- 

 served that amber, called "electron" by them, when 

 rubbed would pick up bits of paper or other light ob- 

 jects. Centuries later Gilbert called these mysterious 

 things "electric." Today, thanks to modern scientific 

 methods, we know more about electricity, but we are 

 only beginning to understand what it really is. 



It is seldom, unless we are "shocked," that we give 

 any thought to the tremendous amount of energy that 

 lies at our finger tips. Rarely do we marvel or wonder 

 at the doings of this invisible but faithful servant. But 

 take it away and we should be set back a hundred 

 years in progress. For all the conveniences, not only 

 of electricity but of all applied science, we are in- 

 debted to the past and obligated to the future. The 

 modern servant, electricity, would not have been pos- 

 sible had not Gilbert, Franklin, Galvani, Volta, Davy, 

 Oersted, Ampere, Ohm, Wheatstone, Faraday, Henry, 

 Gramme, Maxwell, Kelvin, Morse, Bell, Edison, Mar- 

 coni, Fleming, DeForest, and others spent years of 

 thought and experimentation, often under great priva- 

 tion, to perfect its control. 



Our obligation to the past is to know the great ef- 



fort that has brought electricity to its present state of 

 development. Our obligation to the future is twofold : 

 first, to conserve the present supplies or natural 

 sources of energy, that the future may benefit from 

 them also; second, to push back the frontiers of 

 knowledge that the mysteries of electricity may be 

 better understood. 



In the study of this unit we want you to learn how 

 magnetism is related to electricity, how Faraday dis- 

 covered a way to change mechanical energy to electri- 

 cal energy, and how electricity is put to use in the 

 home. 



The exercises that follow should help you to see 

 how much you know about the subject to be studied 

 and should raise some questions in your mind that you 

 will wish to answer through study. 



What do you know about electricity? 



1. Rub a hard rubber comb or fountain pen on the 

 sleeve of a woolen coat or dress and explain what hap- 

 pens when the comb or pen is brought near bits of 

 paper or cork. 



2. Secure a steel needle and run it lengthwise 

 through a cork. Float the needle and cork in a glass 

 of water and bring a magnet near. Explain what hap- 

 pens. Stroke the point of the needle with the end of 

 the magnet marked 6" and replace it on the water. 

 Remove the magnet and explain what happens. 



3. Examine the device which turns an electric wash- 

 ing machine or sewing machine. What is it called? 

 How does electricity make it turn and do work? 



4. Snap the electric switch in your room. Why does 

 the light go out? 



5. Examine an electric toaster. Why do the wires 

 get hot? 



6. Find the electric meter in your house and make 

 a diagram sketch of every detail on the face, including 

 the printing. Can you explain what the printing means 

 and can you read the dials? 



TOPIC 1. SOME WAYS OF SECURING ELECTRICAL ENERGY 



SUGGESTED PROBLEMS AND QUESTIONS 



1. What is electricity? 



2. How may electricity be obtained by friction? 



3. How is electrical energy secured from chemi- 

 cal energy? 



SUGGESTIONS AND HELPS FOR STUDY 

 1. Carefully study the problems listed above and 

 see if they are questions which you have wondered 

 about or are interested in. 



2. If you experiment with the simple voltaic cell 

 or storage battery, be very careful not to get the sul- 

 phuric acid on your hands or clothing. 



3. In the study of this topic you may meet the fol- 

 lowing words for the first time. Study them carefully 

 and use them as frequently as possible in order that 

 they may become a part of your vocabulary. 



ammonium chloride a salt-like substance which con- 

 tains nitrogen, hydrogen, and chlorine and is used in 

 dry cells. 



atom the smallest particle of an element. 



239 



