232 Common Science 



wire that is used in electric irons and toasters and heaters. 

 It has so great a resistance to the electricity that it is 

 heated red hot, or almost white hot, by the electricity 

 passing through it. 



Application 57. A power company wanted to send large 

 quantities of electricity down from a mountain. Should the 

 company have obtained resistance wire or copper wire to 

 carry it? Should the wire have been large or fine? 



Application 58. A firm was making electric toasters. In 

 the experimental laboratory they tried various weights of 

 resistance wire for the toasters. They tried a very fine 

 wire, No. 30 ; a medium weight wire, No. 24 ; and a heavy 

 wire, No. 18. One of these wires did not get hot enough, 

 and it took so much electricity that it would have been too 

 expensive to run ; another got so hot- that it soon burned 

 out. One worked satisfactorily. Which of the three sizes 

 burned out? Which was satisfactory? 



Inference Exercise 

 Explain the following : 



341. If you attach one end of a wire to a water faucet and connect 



the other end to an electric lamp in place of one of the regu- 

 lar lighting wires, the lamp will light. 



342. The needle of a sewing machine goes up and down many times 



to each stroke of the treadle. 



343. Trolley wires are bare. 



344. If you had rubbers on your feet, you could take hold of one 



live wire with perfect safety, provided you touched nothing 

 else. 



345. If you were on the moon, you would look up at the earth. 



346. Toy balloons burst when they go high up where the air is 



thin. 



347. You have to put on the brakes to stop a car quickly. 



348. Telephone wires are strung on glass supporters. 



349. If you pour boiling water into a drinking glass, frequently 



the glass will crack. 



350. An asbestos mat tends to keep food from burning. 



