Applied Electricity Paper 2 , Nov/Dec. 2012  
Questions:   1 2 3 4 5 6   Main
General Comments

Question 2

(a) State two factors that affect the flux density of a magnetic core.
(b) A magnetic core has a coil of 500 turns wound on it. If a current of 5 A is
passed through it and the length of the core is 100 em, calculate the:
      (i)        magnetomotive force;
      (ii)        magnetizing force;
      (iii)       magnetic flux density if the permeability of the core is 16 rr x 10-7




The expected answers were:
(a) Any two of the factors stated below
Change in flux;
Change in cross-sectional area;
Change in permeability of the core;
Change in magnetising force.
(b) (i) m.m.f. = IN
=5 x 500 = 2500 AT
       (ii)            magnetising force, H = l~
= ~ = 2500 AT/m
       (iii)           B = pH
= 16rr x 10-7 x 2500 = 0.0126 T
The question was on Electr9magnetic Field. The question was unpopular with
the candidates. The candidates' performance was not encouraging.



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