Electricity 213 



A conductor is a substance through which an electric charge 

 passes readily. An insulator is a substance through which an 

 electric charge will not pass. 



A condenser is a device by means of which electrical charges 

 are accumulated. A Leyden jar is a condenser. 



Lightning is a discharge between two clouds bearing unlike 

 electrical charges, or between charged clouds and oppositely 

 charged objects on the earth. 



The electron theory assumes that the atoms of all substances 

 contain electrons of negative electricity and protons of positive 

 electricity. 



Current electricity means flowing electricity. 



An electric cell is a device for the production of electricity by 

 chemical action. 



The circuit is the course an electric current takes in its com- 

 plete passage from some point back to the same point. 



Dry cells differ from wet cells in having the chemicals in the 

 form of a moist paste instead of in a liquid. 



Storage cells have plates of lead. Such cells are used to 

 store electric energy from an electric current, in the form of 

 chemical energy. 



Electrical resistance is the term applied to the amount of diffi- 

 culty a current has in passing over conductors and through instru- 

 ments. 



Ohms, volts, amperes and watts are units used in measuring 

 electricity. 



FACT AND THOUGHT QUESTIONS 



1. Upon what properties does electricity depend for its value in doing 

 work? 



2. Give two simple experiments that illustrate the action of static elec- 

 tricity. 



3. Describe the electroscope and state its purpose. 



4. State the difference between a conductor and an insulator and give 

 examples of each. 



5. Define potential. 



6. Describe the Leyden jar. 



7. State the electron theory. 



8. Describe an electric cell. 



