Question 3
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AIM: To test candidates’ knowledge of circuit laws.
(a) Connect the circuit as shown in Fig. 1.
(b) Ask the supervisor to check the circuit connection.
(c) Set the power supply to 9V.
(d) Close the switch Sw.
(e) Set the current, I, to a value of 5mA by adjusting the potentiometer.
(f) Read and record in Table 3, the corresponding values of voltages of V1 and V2.
(g) Repeat steps (e) and (f) for other values of I in Table 3.
(h) Open switch Sw.
(i) Complete Table 3.
Table 3
S/NI(mA)
V1(V)
V2(V)
Vpot = 9 – (V1 + V2)
(j) Plot a graph of Vpot (V) on the vertical axis against I (mA) on the horizontal axis.
(k) Comment on the shape of the graph.
(l) State one law verified by this experiment.
(m) State two precautions taken in carrying out this experiment.
Observation
Table 3
S/N |
I (mA) |
V1 (V) |
V2 (V) |
Vpot = 9 – (V1+V2) |
1 |
5 |
0.5 |
0.75 |
7.75 |
2 |
10 |
1.0 |
1.50 |
6.50 |
3 |
15 |
1.5 |
2.25 |
5.25 |
4 |
20 |
2.0 |
3.00 |
4.00 |
5 |
25 |
2.5 |
3.75 |
2.75 |
(j) Graph with correct:
(i) title of graph;
(ii) points of values;
(iii) line of best fit;
(iv) scale for x and y axes;
(v) labeling of axes with units.
(k) Comment on shape of graph
- Vpot is inversely proportional to I(mA).
- The higher the value of Vpot, the lower the value of I(mA).
- The lower the value of Vpot, the higher the value of I(mA).
(l) Law that verifies the experiment
- Ohm’s law/V=IR
- Kirchhoff’s Voltage Law (KVL)
(m) Precautions in carrying out the experiment
- I ensured constant power supply in the course of the experiment.
- I ensured proper soldering to avoid dry joints.
- I ensured correct polarity of meters.
- I ensured proper setting of scales/ranges of meters
- I ensured tight connections.
Candidates were expected to take readings accurately with the specified measuring instruments and draw graph with the correct title of graph, points of values, line of best fit, scale for x and y axes and labeling of axes with units. A few candidates failed to respond to question as expected.