44 



ELECTRICAL ENGINEERING 



Fig. 37 shows the magnetic fields produced in certain cases. 

 The lines of induction are all closed lines and extend from a 

 north to a south pole in air and from a south to a north pole in- 

 side the magnetic material or the generator of m.m.f . 



(a) Field of a Bar Magnet 



( 6 ) Field of a Solenoid 



(c) Field near anlsolated North Pole ( d) Field of a Dynamo 



FIG. 37. Magnetic fields. 



33. Magnetic Flux. The total number of lines of magnetic 

 induction passing through a given section is called the magnetic 

 flux through the section and is represented by 3>. 



The unit of magnetic flux, which is one line, is called the max- 

 well. 



Flux from Unit Pole. At every point on a sphere of one centi- 

 meter radius, surrounding a unit pole as centre, a similar unit 

 pole is repelled with a force of one dyne. There must therefore 

 be one line of induction per square centimeter passing through 

 the surface, and since the surface is 4 TT sq. cm. the total flux from 

 the unit pole is 



$ = 4 TT lines. 



The flux from a pole of strength m is 

 3> = 4 irm lines. 



