- Measure and record the emf, V\(_{o}\) of the cell provided.
- Connect a circuit as shown in the diagram above.
- With the key, K closed vary the rheostat, Rh to obtain a current 1 = 0.20A. Read and record the corresponding value of the potential difference, V on the voltmeter.
- Evaluate 1\(^{-1}\) and V\(^{-1}\).
- Repeat the procedure for four other values of l = 0.25, 0.30, 0.35 and 0.40 A. Tabulate your readings.
- Plot a graph V\(^{-1}\) on the vertical axis against 1\(^{-1}\) on the horizontal axis.
- Determine the slope, s, of the graph
- Evaluate s\(^{-1}\).
- State two precautions taken to ensure accurate results.
(b)i. Explain Ohmic conductor:
ii. Explain resistivity of the material of a wire.
Explanation
1. v\(_{o}\) = 3.0v
2. V\(_{R}\) = 0.20 volts
3. l = 0.20, 1\(^{-1}\) = \(\frac{1}{1} = \frac{1}{0.2}\) = 5
V = 0.2, V\(^{-1}\) = \(\frac{1}{V} =\frac{1}{0.2}\) = 5
Table of values/observations
| S/N | IA | I\(^{-1}\)(A\(^{-1}\)) | V(volts) | V\(^{-1}\)(volts\(^{-1}\)) |
| 1 | 0.20 | 5.00 | 0.19 | 5.26 |
| 2 | 0.25 | 4.00 | 0.23 | 4.35 |
| 3 | 0.30 | 3.33 | 0.28 | 3.57 |
| 4 | 0.35 | 2.86 | 0.33 | 3.03 |
| 5 | 0.40 | 2.50 | 0..38 | 2.63 |
Slope (s) = \(\frac{\bigtriangleup {V}^{-1}}{\bigtriangleup {I}^{-1}}\)
S = \(\frac{5.1-1.0}{4.55-12} = \frac{4.1}{3.35}\) = 1.224
S\(^{-1}\) = \(\frac{1}{s} = \frac{1}{1.224}\) = 0.817
N.B: R = S\(^{-1}\) = 1.0
Precautions taken to ensure accurate results are as follows
- Tight connections ensured/clean terminals
- Repeated readings have been shown on the table
- Parallax error in reading voltmeter/ammeter avoided
- Key open when reading is not being taken
(b)i. An ohmic conductor is s Conductor in which the current passing through it is proportional to the p.d across the conductor, provided temperature and other physical conditions are constant.
ii. The resistivity of the material of a wire is the resistance of a unit length of the wire of unit Crofs sectional area. It is denoted by p. and measured in ohm-metre (L-m).