Applied Electricity Paper 2 , Nov/Dec. 2011  
Questions:   1 2 3 4 5 6   Main
General Comments

Question 5

  1.           State:
         (i)       Faraday’s law of electromagnetic induction;
         (ii)      one application of Faraday’s law of electromagnetic induction.
    (b)     An a.c. generator has 10 poles. Calculate the number of:

    1. cycles generated in 1 revolution;
    2. revolutions per second required to generate a voltage at a frequency of 50 Hz.




The expected answers were:

(a)      (i)      Faraday’s law of electromagnetic induction states      
                   that the magnitude of the induced e.m.f. is proportional to the
                    rate at which the conductor cuts or is cut by the magnetic flux
          Faraday’s law states that the magnitude of the e.m.f. induced in a
          circuit is proportional to the rate of change of magnetic flux
          through the circuit.

(ii)      Electric bells, buzzers, telephone receivers, loudspeakers and

  1. (i)       2 poles give 1 cycle: 1 revolution

          10 poles give 1 x  = 5 cycles

(ii)       T(revolutions per second) =  =  = 20 mS
The question was on Electromagnetic Fields/A.C. Machines. The question was well attempted by the candidates. However, the (b) part was not well done by many; attributed to level of understanding and exposure.




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