Basic Electronics Paper 3, WASSCE (PC), 2016

Question 2

 

 

  1. Connect the circuit diagram as shown in Figure 2.
  2. Ask the supervisor to check the circuit connection.
  3. Copy Table 2 into your answer booklet.                                                 

Table 2
           

 

  1. Switch on the power supply unit.
  2. Set the power supply unit to 9V.
  3. Adjust the potentiometer to set the value of Ib to 100 µA.
  4. Read and record the corresponding values of Ic and VCE.
  5. Repeat steps (f) and (g) for the other values of Ib.
  6. Switch off the power supply unit.
  7. Comment briefly on the values of Ic against the values of Ib and VCE.

The candidates were expected to connect the circuit as shown, measure and record the values as indicated in Table 2. Interpretations and deductions were expected to be from the values recorded by respective candidates only.

Observation

The expected answers were:

  1.             Table 2

     


    Ib (mA)

    Ic (mA)

    VCE (V)

    100

    18.890

             0.121

    150

    18.947

    0.095

    200

    18.973

    0.082

    250

    18.991

    0.074

    300

    19.000

    0.067

    (j)   (i)         As Ib increases Ic remains constant.

          
    (ii)        As Ib increases VCE decreases.              
    Some of the candidates could not perform experiment 2 and a few were unable to make 
    proper deductions .