INDUCED CURRENTS 



155 



7. State the Law of Magnets. How do both poles act toward 

 unmagnetized iron ? 



8. Why does the compass needle point steadily in one direc- 

 tion? Where is the north magnetic pole? Is it positive or 

 negative ? 



SECTION V 

 INDUCED CURRENTS 



179. Induced Electro-Motive Force. It has been found 

 that currents can be produced by means of a magnet, 

 and the electric currents so made are called induced 

 currents. The 

 very powerful 

 currents now in 

 common use are 

 induced currents, 

 and for this reason 

 it is interesting 

 to learn how they 

 are produced. 



Experiment 106. 

 Balance a thin 

 card upon the two 

 ends of a horseshoe 

 magnet, and sprinkle 

 iron filings evenly over the card. Note the positions taken by 

 the filings. 



The arrangement of the filings on the card shows the 

 position of " lines of force " in the field between the 

 poles of the magnet (Fig. 113). Now, if a circuit of 

 wire be moved in such a magnetic field, a current will 

 flow in this circuit while there is a change in the number 



PIG. us 



