CHAPTER XXXIV 



HOW ELECTRICITY MAY BE MEASURED 



312. Danger of an Oversupply of Current. If a small toy 

 motor is connected with one cell, it rotates slowly; if con- 

 nected with two cells, it rotates more rapidly, and in general, 

 the greater the number of cells used, the stronger will be the 

 action of the motor. But it is possible to send too strong 

 a current through our wire, thereby interfering with all mo- 

 tion and destroying the motor. We have seen in Section 

 288 that the amount of current which can safely flow through 

 a wire depends upon the thickness of the wire. A strong 

 current sent through a fine wire has its electrical energy 

 transformed largely into heat ; and if the current is very 

 strong, the heat developed may be sufficient to burn off the 

 insulation and melt the wire itself. This is true not only of 

 motors, but of all electric machinery in which there are cur- 

 rent-bearing wires. The current should not be greater than 

 the wires can carry, otherwise too much heat will be developed 

 and damage will be done to instruments and surroundings. 



The current sent through our electric stoves and irons 

 should be strong enough to heat the coils, but not strong 

 enough to melt them. If the current sent through our electric 

 light wires is too great for the capacity of the wires, the heat 

 developed will injure the wires and may cause disastrous 

 results. The overloading of wires is responsible for many 

 disastrous fires. 



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