Basic Electricity Paper 3 , Nov/Dec 2014
 Questions: 1 2 Main
General Comments
Weakness/Remedies
Strength

Question 2

AIM: To verify Ohm’s law in a series d.c circuit.

VS = 5 V

 Quantity Measured value RT Total current, IT Supply voltage VR3 VR4

Table 3

VS = 10 V

 Quantity Measured value RT Total current, IT Supply voltage VR3 VR4

1.   Adjust the power supply to 5 V.
2.   Close switch S.
3.   Measure the total resistance RT and record in Table 2.
4.   Measure the supply voltage across PQ and the voltage drop across each of

the resistors R3 and R4 and record the results in Table 2.

•   Read and record in Table 2 the ammeter reading (IT).
•   Open switch S.
•   Adjust the power supply to 10 V.
•   Repeat steps (e) to (i) and record all the readings in Table 3.
•   Compare (VR3 + VR4) (V) with Vs(V) in Table 2.
• Compare (R3 + R4) Ω with RT Ω in Table 3.
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Observation

The candidates were expected to connect the circuit as shown in Figure 1, measure and record in Tables 2 and 3 the expected readings. They were also required to evaluate some quantities and do some comparisons.
The expected answers were:
(c)                                           Table 2

VS = 5 V

 Quantity Measured value RT 2174 Ω Total current, IT 2.30 mA Supply voltage 5V VR3 2.25 V VR4 2.75 V

Table 3

VS = 10 V

 Quantity Measured value RT 2.2 kΩ Total current, IT 4.60 mA Supply voltage 10 V VR3 4.50 V VR4 5.50 V

(l)         The two voltages are same
(m)       The two resistances are same
Candidates did well in this question. Majority of them obtained more accurate readings than in Question 1.

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