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.

Connect the circuit as shown in Figure 2.
Ask the supervisor to check the circuit connection.
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.

_____________________________________________________________________________________________________

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

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.