322 



Introduction to the Study of Science 



of the direction of the electric current at the critical points, the 

 coil known as the armature will continue to rotate. The chief 



difference between this sim- 

 ple form and an actual motor 

 is in the strength of the mag- 

 net and the number of coils 

 I of wire the actual motor has 

 to form the armature. 



The essential facts in the 

 structure and operation of the 



FIG. 101. A simple form of the elec- electric motor may be learned 



^ examining a small model 



motor, or better still by mak- 

 ing a motor, for which the following plan may serve. Careful 

 study of the motor will prepare the way for an understanding 

 of the generator. 



Design for a motor. The framework (Fig. 102) is made of two 

 iron bars (/, B} about \" by If" by 12" long, and two iron bolts about 

 \" diameter by 10" long, around each of which should be an iron 

 sleeve 8" long (a piece of iron pipe of f" inside diameter). The iron 

 bolts with iron sleeves serve as the cores for what is called the field 

 coil. Wrap the pipe with insulating tape, and then with three layers 

 of insulated copper wire, No. 22, Brown and Sharp gauge, insulating 

 with tape between each layer. 



The rotating part, which is called the armature (A), is made of 

 a wooden wheel about 6" in diameter. Make a coil of soft iron wire 

 (stovepipe wire) in the form of a circle about seven inches in diameter 

 and as thick as a half inch rod. Wrap the coil with insulating tape. 

 Mark it off into four equal segments and wrap each with a single 

 layer of No. 22 insulated copper wire. The wire may be kept un- 

 broken between the segments as in the diagram. Fasten the wrapped 

 coil to the wooden wheel by nailing and wedging. 



Cut a three inch disk of sheet copper into quarters and fasten them 

 (C, C, C, (7) to the armature with small nails. The wood is sufficient 

 insulation between the segments. Connect the ends of the armature 

 coils of wire, making clean connections (A, C), to the segments of 

 copper. The copper segments form what is known as the commutator. 



Support the wheel upon a nail of suitable length. Provide a high 



