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ELEMENTS OF GENERAL SCIENCE 



is reversed in the loop the north pole of the compass will 

 be deflected in the opposite direction. The different posi- 

 tions given above make it possible to find the direction in 

 which a direct current is flowing. Current detectors of this 

 variety can be made also by placing the magnet in a fixed 

 position and arranging a movable coil with a pointer. 



FKJ. 113. Demonstration materials for studying electromagnets 



The coils are connected in series and carry a current of one ampere. From left to 

 right : bar magnet ; three coils of wire wound upon iron cores, the whole serving as 

 magnets (the U-core when wound becomes a relatively strong magnet) ; the elec- 

 tromagnet of a small motor; the electromagnet of a larger motor or dynamo. 

 The adhering nails indicate the region of magnetic action, or lines of force 



That a coil of wire carrying a current is a magnet is 

 further illustrated in figure 113. The bar magnet stands per- 

 pendicular to the board when no current flows through the 

 coils, which are connected in series. The instant the switch 

 is closed the magnet swings and takes the position shown, 

 indicating that the coil of copper wire has become a magnet. 

 The compass shows that one side of this coil is an N pole 

 and the other an S pole. When the circuit through the coil 

 is opened, the bar magnet returns to its original position. 



