Radio,Television And Electronic Paper 2, WASSCE (SC), 2017

Question 4

     

  1. (i) Define rectification.

(ii)Fig. 5 is a fragment of a block diagram of a power supply unit.

Using Fig. 5, complete Table 1.
Table 1

 

Name of block

Function

X

 

 

Y

 

 

   

  1. State the difference between a half-wave recitifer and a bridge rectifier in relation to:
  2. number of diodes used;
  3. frequency of the output signal.

 

 

  1. Fig. 6 is a series RLC circuit at resonance.


Calculate the resonance frequency.

     

     

 

Observation

The expected answers were:

(a) (i) Rectification is the process of converting alternating current (a.c.) to direct current (d.c.).

     (ii)                                                 Table 1

 

Name of block

Function of block

X

Transformer

  • Isolates the circuit from mains/supply
  • Steps down voltage

Y

Filter

  • Remove ripples/pulses from signal/smoothens signal

                                                                                        
(b) Differences between half-wave rectifier and bridge rectifier
(i) half-wave rectifier uses one diode and bridge rectifier uses four diodes          
(ii) frequency of the output signal is the same as input signal in half-wave rectifier while the 
frequency is twice the input signal in bridge rectifierOR  fo = 2fin
(c)      
 
    
Many candidates did not respond well to this question.