You have been provided with a resistance box, a voltmeter, a key, a battery, and other necessary materials.
- Connect the circuit as shown in the diagram above.
- With the key K closed, read and record the voltmeter reading V\(_{0}\).
- Set the resistance R in the resistance box equal to I\(\Omega\).
- Close the key, read and record the potential difference V on the voltmeter.
- EvaluateR\(^{-1}\) and V\(^{-1}\) .
- Repeat the procedure for five other values or R = 2\(\Omega\), 3\(\Omega\), 4\(\Omega\), 5\(\Omega\) and 6\(\Omega\).
- Tabulate your readings.
- Plot a graph with V\(^{-1}\) on the vertical axis and R on the horizontal axis.
- Determine the slope, s, of the graph and the intercept, C, on the vertical axis.
- Evaluate c\(^{-1}\)
- State two precautions taken to obtain accurate results.
(b)i. Define the potential difference between two points in an electric circuit.
ii. Explain why the emf of a cell is greater than the p.d. across the call when it is supplying Current through an external resistance.
Explanation
| S/N | R/W | V/vat | R\(^{-1}\)/W\(^{-1}\) | V\(^{-1}\)/vat |
| 1 | 1.0 | 1.80 | 1.00 | 0.56 |
| 2 | 2.0 | 2.10 | 0.50 | 0.48 |
| 3 | 3.0 | 2.30 | 0.33 | 0.43 |
| 4 | 4.0 | 2.40 | 0.25 | 0.42 |
| 5 | 5.0 | 2.50 | 0.20 | 0.40 |
| 6 | 6.0 | 2.60 | 0.17 | 0.30 |
Slope = \(\frac{0.65 - 0.40}{1.10 - 0.20} = \frac{0.25}{0.9}\)
= 0.3
X = c = 0.35 = C\(^{-1}\) = 2.86
Precautions; I
- ensured that the key was open after each reading so that the battery will not run down quickly.
- ensured there was no Zero error when taking the voltmeter reading.
- ensured the electrical wire was tightly connected to the terminals in order to avoid current fluctuations.
(b) i. Potential difference is the amount of work done in moving a unit positive charge from a point to another, mostly from a point of lower potential to the point of higher potential. Its density p.d. measured in Volts.
ii. The e.m.f. of a cell is the p.d. across the terminals when it is in an open circuit i.e. hot supplying current to an external circuit. While terminal p.d. 5 is defined as the p.d, between the terminals of a cell when it is delivering current to an external circuit. Therefore, emf is greater because it has not yet been connected to an external circuit.
