Applied Electricity Paper 2 , May/June 2011  
Questions:   1 2 3 4 5 6   Main
General Comments

Question 2
  1. State:
  2. Lenz’s law;
  3. three applications of electromagnetism.
  4.  A conductor, 0.4 m in length, moves with uniform velocity of 3 m/s at right   angles to a uniform magnetic field having a flux density of 1.5 T. Calculate  the induced e.m.f.


The expected answers were:

  1. (i)  Lenz’s law states that the direction of an induced e.m.f. is always such      that it tends to set up a current opposing the motion or the change of flux      responsible for inducing that e.m.f.

          Lenz’s law states that the direction of an induced e.m.f. tends to oppose           the cause.
    (ii)   Any three of the following applications were acceptable:
          Electric bells                                        Circuit breaker
          Electric fan                                          Ignition assembly
          Transformer                                        Miniature Circuit Breaker
          Contactor                                            Solenoid
          Electric motor                                      Buzzers
          Telephones                                          Radio receivers
          Loudspeakers                                       Relays

  1.  l = 0.4 m, v = 3 m/s , B = 1.5 T

e = Blv sin
   = 1.5 x 0.4 x 3 sin 900
   = 1.8 V.

The question was on Electromagnetic Field. The question was popular with the candidates. The performance was reported to be above average
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