362 HOW ELECTRICITY IS CONTROLLED 



they are more convenient to handle, have come to replace 

 to a large extent the wet cell in our homes. 



What produces the electric current ? When an 

 electric cell has been used for a long time, it may refuse to 

 produce any more current. In the case of the wet cells, 

 you will very likely find that one of the plates in it has 

 been used up. This suggests that some vigorous chemical 

 action has taken place in the cell between the solution and 

 the plates. This is true. The cell is really a device by 

 which energy resulting from this chemical action in the 

 cell is changed into electrical energy. 



Experiment. To make a wet cell and show presence of electric current. 



Materials: Carbon. Zinc. Jar for sal ammoniac cell. Sal ammoniac. 

 Electric bell or compass. Wires. 



Method: Fill the jar with water to the mark and add sal ammoniac 

 and stir. Continue adding sal ammoniac until a saturated solution 

 is obtained. Put zinc and carbon in cell. Join wires to poles. Test to 

 see if a current is produced by joining an electric bell in circuit or 

 test wire of closed circuit with compass. How can you detect a current 

 in a wire by means of a compass? 



Result and Conclusion: What is the result? What are the essentials of 

 a wet cell? 



Wire resistance to electricity. Anybody knows that 

 if he wants to empty a tank of water a short pipe would 

 empty it quicker than a long one of the same diameter. 

 This is explained by the fact that a long pipe has more 

 surface to rub against the flowing water, and this produces 

 iriction, thus allowing less water to get out in a given time. 

 There is a very close parallel to this in the case of elec- 

 tricity passing through wires. If you connect the poles 

 of one cell with a long wire and then the poles of the other 

 cell with a shorter wire of the same diameter, the elec- 

 tricity will be discharged through the shorter wire more 



