Applied Electricity 1, Nov/Dec 2011
 Questions: 1 2 Main
Weakness/Remedies
Strength

Question 1

AIM: To determine how voltages are distributed in resistor circuits according to Ohm’s law.

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

Table 1

 V(V) 0 2 4 6 8 10 12 I(A)

1.   Close switch S.
2.   Set the power supply to 0 V.
3.   Read and record the ammeter reading in Table 1.
4.   Increase the voltage value in steps of 2 V to 12 V and record the

corresponding ammeter readings in Table 1.

1.   Plot a graph of voltage V(V) on the vertical axis against current I(A) on

the horizontal axis.

1.   Determine the slope of the graph.
2.   Deduce from the graph the value of the unknown resistance X.

The candidates were expected to connect the circuit as shown in Fig.1, measure and record in Table 1 the, voltmeter readings, ammeter readings, plot some graph, determine the slope and unknown resistance from the graph.

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Observation

The expected answers were:
Table 1

 V(V) 0 2 4 6 8 10 12 I(A) 0 2 x 10-3 4 x 10-3 6 x 10-3 8 x 10-3 10 x 10-3 12 x 10-3

1. The slope of the graph is 4 kΩ.
2. The deduction is that the slope of the graph is the same as the unknown  resistance X.

The candidates, as reported, understood the question and carried out the actions required. But unfortunately, some of the candidates did not record accurate readings, so their graphs and comparisons were wrong.