waecE-LEARNING
Applied Electricity 1 , May/June 2011  
Questions:   1 2   Main
General Comments
Weakness/Remedies
Strength


Question 2

AIM: Determination of the capacitance of a capacitor using Ohm’s law.

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

Table 2

      Rb(Ω)

      V(V)

       A(A)

       100

 

 

       125

 

 

       150

 

 

       175

 

 

       200

 

 

 

 

 

 

4.Set Rb to 100 Ω.

5. Close switch S.

6. Read and record the readings on ammeter A and voltmeter V in Table 2.

7. Open switch S.

8. Increase Rb in steps of 25 Ω and repeat steps (e) to (g) for each setting  of Rb up to 200 Ω.

9. Plot the graph of V(V) on the vertical axis against A(A) on the horizontal  axis.

10. Determine the slope of the graph.

11. Determine the capacitance, C of the capacitor.

 

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Observation

The candidates were expected to connect the circuit as shown in Fig.2, measure and record in Table 2 the ammeter readings and voltmeter readings. They were also required to plot a graph of voltage V (V) against current A (A) and determine the capacitance of the capacitor in question using Ohm’s law.

The expected answers were:
(c)                                   Table 2


      Rb(Ω)

      V(V)

       A(A)

       100

    11.446

      0.036

       125

    10.158

      0.032

       150

      9.435

      0.030

       175

      8.723

      0.027

       200

      7.294

      0.026

                  

  1. Determination of the capacitance, C of the capacitor

xc =     where XC = slope

                                                     =
                                                  C = 9.9633 x 10-6 µF  10 µF
Candidates again shortchanged themselves with inaccurate readings which greatly affected their performances as earlier reported in Question 1.

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