Basic Electronics Paper 2, WASSCE (SC), 2022

Question 2

 

  1. (a)    Explain the term resonance in a series RLC circuit.
    (b)    Figure 2 is a series RLC circuit.


                                                  
                                                                           Figure 2

    If the impedance of the circuit is 120 Ω at a frequency of 65 Hz, calculate the:

    1. inductive reactance;
    2. capacitance of the capacitor.

     

Observation

   

The expected responses were:

(a)          Resonance occurs when the inductive and capacitive reactance are equal in magnitude.  

(b)          (i)        XL        =          2π f L                                                                                         
=          2π × 65 × 30 × 10-3                                                                    
                           =          12.25 Ω                                                                                      

   (ii)       XC       =                                                                                                      
               Since Z = 120 Ω = R
Then,      | XC |    =          | XL |                                                                               
                            XC      =          12.25 Ω
12.25   =                                                                                              
C         =         
=          199.9 x 10-6 F
               C         =          0.0002 F          =          200

Question 2 required candidates to explain resonance and also calculate the inductive reactance and capacitance of a capacitor. According to the Chief Examiner, while majority of the candidates could explain resonance, only few could perform the calculation as required.