258 



ELECTRICITY 



Meister, Magnetism and Electricity 

 Morgan,' The Boy Electrician 



WHAT YOU SHOULD AIM TO ACQUIRE FROM 

 THIS STUDY 



1. How fuses are constructed, how they burn out, and 

 how to replace them. 



2. How electric devices are constructed and how they 

 work. 



3. How electric-light bulbs are constructed and how 

 they work. 



4. Something about the invention of the electric light. 



5. How electric motors are constructed and how they 

 work. 



TEST OF MASTERY OF THE TOPIC 



In your notebook complete the statements and answer 

 the questions. 



1. Fuses are made of 

 substances with melt- 

 ing points. 



2. Fuses are rated in 



3. When replacing fuses 

 one should first 



4. In Figure 411 the 



type of fuse is shown 



at A and the type at 



B. 



5. The heating effect of 

 electric currents is due to 

 the of the 



6. Fuses have to 



prevent danger from fire 

 when they burn out. 



7. The element of elec- 

 tric heating devices is usually made of 



8. The part of the electric bulb shown at A in Figure 

 412 is called the and is made of 



9. The terminals are 

 shown at . and 



10. C is made of . 



11. . . has been 



moved 

 shown 



from 

 at E 



re- 

 the space 

 to prevent 



12. 



times 



gas is 



used in the 



some- 



space 

 shown at E. 



13. The parts marked G 

 ___ the filament. 



14. F is a . 



15. The moving part of 

 an electric motor is called 

 the 



16. The field for 



the motor is supplied by 

 magnets. 



17. The electric motor 



changes energy into 



energy. 



18. Motors which have 



a commutator use _ _ current. 



TIG. 412 



19. The push or pull between two 

 _ of the motor to rotate. 



fields causes the 



20. What are the principal advantages around the home 

 in the use of heat secured from electricity? What are the 

 disadvantages ? 



21. A new type of light recently developed for lighting 



and is known as the vapor lamp. Its chief 



disadvantage for indoor illumination is 



22. Another device used to transform electrical energy 

 to light energy is known as the lamp. In it current 



is carried across a gap between two 



electrodes by 



vapor. The light of this lamp is supplied by the heating to 

 of tiny particles of drawn out of the electrodes. 



TOPIC 5. HOW ELECTRICITY IS MEASURED 



SUGGESTED PROBLEMS AND QUESTIONS 



1. How are electric currents measured? 



2. What important law governs electric cur- 

 rents? 



3. How is the cost of electricity determined? 



SUGGESTIONS AND HELPS FOR STUDY 



1. Carefully study the problems to see if they in- 

 clude questions which you have wondered about or 

 are interested in. 



2. In this exercise you will learn a very important 

 law of electricity known as Ohm's Law. It was dis- 

 covered by George S. Ohm, a German scientist, who 

 lived about a century ago. You should be sure to 

 understand this law. 



3. You will learn how to calculate the cost of elec- 

 tricity used in the home. Learn to read an electric 

 meter if you have not already done so. 



4. You may encounter the following new words 

 and phrases in this study. Use them as frequently as 

 you can in order that they may become a part of 

 your vocabulary. 



ampere the unit of current flow in electricity. 

 volt the unit of electrical pressure. 

 ohm the unit of electrical resistance. 



watt a unit for measuring the rate at which work is 

 done by an electric current. 



kilowatt one thousand watts. 



kilowatt hour the amount of work done in one hour 

 when an electric current is working at the rate of 

 one kilowatt. 



