140 ELECTRICITY 



3. Name any cases of electrically charged bodies that are 

 known to you. Experiment with a rubber comb and report the 

 results. 



4. What two sorts of charges are named? How do two bodies 

 behave toward each other when similarly charged ? How do they 

 act when their charges are unlike ? 



5. What is meant by an induced charge? How is a charge, 

 induced from one body to another ? Does the inducing charge 

 lose some of its electricity in the process ? 



6. How does the induced charge compare with the inducing 

 charge ? State the condition of a charge induced in a body. 



7. Explain the nature of an electric discharge. What must 

 be the relation of two charges before a discharge can occur ? 



8. Compare the potentials of the two charges after the dis- 

 charge. What generally attends a discharge ? State any experi- 

 ence that you have had with discharges ; any that you have seen 

 or felt. 



9. What is lightning? Between what bodies does it usually 

 take place ? When, in the year, is lightning most common ? Why ? 



10. Fully explain the cause of the discharge. How long does 

 it last ? What objects are in most danger of being struck ? 



11. Explain the flash of lightning. What is thunder? Why 

 is it not heard as soon as the flash is seen ? 



SECTION III 

 THE ELECTRIC CURRENT 



162. The Voltaic Cell Most of the devices by which 



man employs electrical energy make use of what is called 

 a current, that is, a stream of electricity passing along 

 a conductor. This electric current is commonly pro- 

 duced in one of two ways, by a dynamo or by a voltaic 

 cell. In this section we shall consider the cell, which 

 generally produces weaker currents than the dynamo. 



