ELECTRICAL MACHINERY 475 



the poles of the magnet is reversed the current is also re- 

 versed. 



3. When an electromagnet is used in place of the per- 

 manent one the same results are noticed. 



4. The induced current is produced by the expenditure 

 of muscular energy and does not weaken the magnet. 



5. When the wire is moved so as to cut the magnetic 

 lines of force at right angles the momentarily induced 

 current is greatest. 



6. The direction of the lines of force is at right angles 

 to the direction of the current in the wire. 



634. Factors upon which the value of induced E.M.F. 

 depends. If the wire in Fig. 355 be very quickly moved 

 across the magnetic lines of force the galvanometer 

 needle will deflect farther than when the wire is moved 

 slowly. Also, if two magnets with their similar poles 

 together are used instead of one and the wire is moved 

 at the same velocity as previously the needle will have 

 a greater deflection. Again, if a coil of wire be used in- 

 stead of a single one the deflection of the needle will be 

 greater. Hence it is obvious that the induced E.M.F. 

 is dependent upon and proportional to the number of 

 magnetic lines cut, the speed or rate at which they are 

 cut and the number of w r ires cutting them. 



635. Currents induced in rotating coils. Instead of 

 cutting the magnetic lines of force of a strong magnet 

 with a single wire let them be cut with a coil of 400 or 

 500 turns. Let the coil be small enough so it will rotate 

 between the poles of a horseshoe magnet. With the 

 coil at right angles to the plane of the poles rotate it 

 180 and note the direction of deflection of the galvanom- 

 eter needle. Rotate the coil the other 180 and bring 

 it to the position from which it started and again note 

 the direction of the deflection of the galvanometer needle. 



