Applied Electricity 1 , May/June 2011
 Questions: 1 2 Main
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.

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.

(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.