458 



ELEMENTS OF ELECTRICAL ENGINEERING. 



to itself at a uniform velocity of 1,000 centimeters per second. 

 The bar points magnetic east and west and the horizontal compo- 

 nent of the earth's magnetic field is 0.2 gauss. How much 

 electromotive force is induced in the bar? Express the result 

 in c.g.s. units and in volts. Ans. 60,000 abvolts or 0.0006 volt. 

 54. The straight metal spoke of a wheel is 40 centimeters long. 

 The plane of the wheel is vertical and magnetic east and west. 

 The horizontal component of the earth's magnetic field is 0.2 

 gauss, (a) How many lines of force does the spoke cut in one 

 revolution ? () How much electromotive force is induced in the 

 spoke when the wheel makes 25 revolutions per second? Ans. 

 (a) 1,005.3 maxwells; (^) 0.000251 volt. 



55, The wheel of problem 54 is replaced by 



I a metal disk 80 centimeters in diameter. 



f* 



What is the electromotive force between the 

 center and the circumference of the disk when 

 its speed is 25 revolutions per second? Ans 

 0.000251 volt. 



56. A wire is bent to form a rectangle 

 AB, Fig. 56^, which is rotated about the ver- 

 tical axis CD at a speed of 25 revolutions per 

 second. The horizontal component of the 

 earth's magnetic field is 0.2 gauss, (a) How 

 much magnetic flux passes through AB when 

 its plane is magnetic east and west ? () How 

 much flux passes through AB one quarter 

 of a revolution later ? (c) What is the aver- 

 age value of the electromotive force which is induced in the 

 wire AB during this quarter of a revolution ? Ans. (a) 480 

 maxwells ; (b) zero ; (c) 0.00048 volt. 



57, A conductor A, Fig. 5/P, perpendicular to the plane of 

 the paper, is caused to move in the direction of one of the arrows. 

 Specify the direction of the induced electromotive force in each 

 of the four cases. 



58, The pole face of a dynamo is 30 centimeters long, parallel 



