Basic Electronics Paper 2 WASSCE (PC), 2019

Question 7



  1. Figure 3 is the switching arrangement of a logic circuit.


    Complete Table 1 using Figure 3 by stating condition of output lamp (F) either as on or off

    S1 S2 S3 Output (F)
    open open open
    open open Close
    open Close open
    open Close Close
    Close open open
    Close open Close
    Close Close open
    Close Close Close

  2. Write the Boolean expression for the output (F) in terms of the inputs S1, S2 and S3.

 


Observation

 

The Chief Examiner reported that only a few candidates obtained full marks in this question. It was also reported that some candidates described the output as ‘open’ and ‘close’ contrary to the instruction of ‘on’ or ‘off’ in the question.


The expected responses were:





(b). Boolean expression

(S1.S2 ) + S3 = F