400 



GENEKAL SCIENCE 



8. Why should the ends of lightning rods be buried deep in the 

 ground? 



9. Why are people killed if they touch a " live " wire? 



10. Why may a man who is fixing a trolley wire touch the wire 

 if he is wearing rubber shoes? 



11. Since the trolley track is the return wire to the dynamo, why 

 is it possible to stand on the track without receiving any injury? 



12. What is the third rail? 



OTHER USES FOR ELECTRICITY 



Ohms. When electricity passes over a wire, the wire becomes 

 heated. This is due to the resistance the wire offers to the current. 



FIG. 279. Make several fuses as directed. Determine the amount of current 

 a long, a short fuse, a wide and a narrow fuse will hold. How do you 

 think 20, 30, 50, ampere fuses are made? 



If a large amount of current is driven through a small wire, the wire 

 becomes very hot because it offers a great deal of resistance. 



The amount of resistance is measured by ohms. (What is an 

 ohm?) 



Wires for carrying a great deal of current must be very large 

 to prevent them from becoming hot. The right sized wire must 



