Basic Electronics Paper 2,WASSCE (PC), 2016

Question 3

  1.  


    (a) Explain the term doping with respect to semi-conductors.
    (b) State the phase relationship between the input and output for each of the following:
    (i) common emitter amplifier;
    (ii) common collector amplifier;
    (iii) common base amplifier.
    (c) List the change carriers in a semi-conductor.       

              The expected answers were:
    (a)        Doping is the process of adding impurity atoms (trivalent or pentavalent)
    to an intrinsic semiconductor.                                                            

    (b)        (i) for common emitter, there is 180º degree phase shift / in anti-phase.      
    (ii) for common base, there is no phase shift / 00  phase shift/ in phase.       
    (iii) for common collector, there is no phase shift/ 00  phase shift/ in phase.

    (c)        Holes and electrons.      

 

Observation

A few Candidates could not recall that for semiconductors, the charge carriers are holes and electrons.