Basic Electronics Paper 2, May/June 2015

Question 5

  1. State two effects each of:
  2. (a) positive feedback; (b) negative feedback.


                       Figure 3 below is a summing op-amp circuit.

  1. In Figure 3, calculate the value of the output voltage (Vout)



       The expected answers were:

(a)        (i)         effects of positive feedback:
(a)  Increases gain
(b)  Increases distortion                                             
(c)  Decreases bandwidth

                                    (ii)        Effects of negative feedback:
(a)  Decreases gain
(b)  Decreases distortion
(c)  Increases bandwidth      



= -(20  +  20)    
=  - 40V                                                              

The question was on Circuit Analysis. It was unpopular with the candidates. As reported, not many of the candidates that attempted it understood the requirements of the question.