You are provided with an ammeter, resistor, key, metre bridge, and other necessary apparatus.
i. Connect a circuit as shown in the diagram above.
ii. Close the key and use the jockey to make contact with AB at N such that AN = d = 25cm
iii. Read and record the ammeter reading.
iv. Evaluate 1\(^{-1}\).
v. Repeat the procedures for values of d = 35cmm, 50cm, 65cm and 80cm. In each case, record I and determine 1\(^{-1}\)
vi. Tabulate your results.
vii. Plot a graph with log on the vertical axis and d on the horizontal axis.
viii. Determine the slope, s of the graph.
ix. State two precautions taken to obtain accurate results.
(b)i. Use your graph to determine the value of d = l = 1.5A.
ii. State two factors that affect the resistance of a wire.
Explanation
| S/N | d(cm) | I(A) | I\(^{1}\)(A\(^{-1}\)) | Log I\(^{-1}\) |
| 1 | 25 | 0.65 | 1.54 | 0.19 |
| 2 | 35 | 0.55 | 1.82 | 0.26 |
| 3 | 50 | 0.44 | 2.50 | 0.40 |
| 4 | 65 | 0.30 | 3.33 | 0.52 |
| 5 | 80 | 0.23 | 4.35 | 0.64 |
vii. Scale: 2cm to 10 units on x-axis
2cm to 0.1 unit on y-axis
viii. Slopes(s) = \(\frac{x_{2} - x_{1}}{y_{2} - y_{1}}\)
= \(\frac{80 -25}{0.64 - 0.20}\)
= \(\frac{55}{0.44}\)
= 125
(ix) Precautions
(a) Key opened in between reading or keys opened when readings were not taken
(b) Tight connections ensured
(c) Avoided parallax error when taking reading on ammeter or metre rule
(d) Repeated readings shown
(e) Avoided zero error on ammeter or metre rule
(f) Clean terminals ensured.
(b)i. 1\(^{-1}\) = \(\frac{1}{1.5}\)
= 0.67
Log(1\(^{-1}\)) =-0.174
ii. Factors affecting the resistance of a wire
- Length of wire
- Cross-sectional area/ thickness/ diameter/ radius of wire
- Resistivity or nature of wire
- Temperature.