You are provided with a variable d.c. power supply E, a 2\(\propto\) standard resistor, a key, an ammeter, a voltmeter and other necessary materials.
i. Set up a circuit as shown in the diagram above with E= 1.5V
ii. Close the key k.
iii. Take and record the voltmeter reading V.
iv. Take and record the corresponding ammeter reading l.
v. Evaluate V\(^{-1}\) and l\(^{-1}\)
vi. Repeat the procedure for four other values of E= 3.0V, 4.5V, 6.0V, and 7.4V.
vii. Tabulate your readings.
viii. Plot a graph with V\(^{-1}\) on the vertical axis and l\(^{-1}\) on the horizontal axis starting both axes from the origin (0, 0).
ix. Determine the slope, s, of the graph.
x. Also determine the intercept, e, on the vertical axis.
xi. State two precautions taken to obtain accurate results.
(b)i. State two methods by which an electric current can be produced.
ii
Calculate the value of R in the circuit diagram shown above, given that the effective resistance of the circuit is 4.0\(\Omega\) and the internal resistance of the cell is negligible.
| S/N | E/v | I/A | V/V | \(\frac{1}{V}\)/V\(^{1}\) | l\(^{-1}\)/A\(^{-1}\) |
| 1 | 1.5 | 0.30 | 0.80 | 1.250 | 3.333 |
| 2 | 3.0 | 0.50 | 0.40 | 0.717 | 2.000 |
| 3 | 4.5 | 0.70 | 2.00 | 0.500 | 1.429 |
| 4 | 6.0 | 0.90 | 2.50 | 0.400 | 1.111 |
| 5 | 7.5 | 1.10 | 3.00 | 0.333 | 0.909 |
Slope = \(\frac{\bigtriangleup {V}^{-1}}{\bigtriangleup {I}^{-1}}\) = \(\frac{V_{2}^{-1} - V_{1}^{-1}}{I_{2}^{-1} - I_{1}^{-1}}\)
= \(\frac{3.333 - 0.800}{1.24 - 0.26}\)
= \(\frac{2.53}{0.98}\) = 2.6
Intercept C = 0.04
Precaution;
- Ensured clean terminals/tight connections
- Key removed after taking each reading/key removed
- when reading was not being taken.
- Avoided parallax error on Voltmeter/Ammeter Noted/corrected zero error on voltmeter/ammeter
- Repeated readings (shown on the table)
(b) Production of electric current e.g. use of
- Cells (accumulators/simple cells) fuel cells (chemical energy)
- Generators/dynamos/electromagnetic induction (mechanical)
- Solar cells/photocells
- Windmills
- Tidal waves
- Geothemal/thermal
- Gas turbines
- Hydro power
- Nuclear power
- Thermocouple/thermopile/themionic (heat energy)
- Piezo electric generators
- Electrostatic generator (e.g Van de graff generator)
ii. \(\frac{1}{Re}\) = \(\frac{1}{R1} + \frac{1}{R2}\)
= \(\frac{1}{R} + \frac{1}{R} = \frac{2}{R}\)
Re = \(\frac{R}{2}\)
RT = \(\frac{R}{2}\) + 2 = 4
\(\frac{R}{2}\) = 4 - 2 = 2
R = 4\(\Omega\)
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