You are provided with a constantan wire, a2 \(\Omega\)standard resistor, an accumulator E, an ammeter A, a key K, and other necessary apparatus.
- Measure and record the emf of the accumulator provided
- Connect a circuit as shown in the diagram above.
- Close the key, read and record the ammeter reading l\(_{o}\) when the crocodile clip is not in contact with the Constantan wire.
- Open the key with the clip making contact with the wire, when d=90cm, close the key. Read and record the ammeter reading l.
- Evaluate d\(^{_1}\)
- Repeat the procedure for four other values of d=80, 70, 60, and 50 cm
- In each case, read and record the ammeter reading and evaluatre d\(^{_1}\).
- Tabulate your readings.
- Plot a graph with I on the vertical axis and d\(^{_1}\) on the horizontal aXIS.
- Determine the slope, S of the graph and its intercept, c, on the vertical axis.
- Evaluate k = \(\frac{c}{s}\)
- Using your graph, determine the current I when d=55cm.
- State two precautions taken to obtain accurate results.
(b)i. Explain what is meant by the potential difference between two points in an electric circuit.
ii. State two factors on which the resistance of a wire depends.
Explanation
| d/cm | I/A | d\(^{-1}\)/cm\(^{-1}\) |
| 80.0 | 0.23 | 0.0125 |
| 70.0 | 0.25 | 0.0143 |
| 60.0 | 0.31 | 0.0167 |
| 50.0 | 0.34 | 0.0200 |
| 40.0 | 40.0 | 0.0250 |
Slope, SI = \(\frac{\bigtriangleup {I}}{\bigtriangleup {d}^{-1}}\) = \(\frac{0.40-0.13}{0.024-0.006}\)
= \(\frac{(0.27)A}{(0.018)cm^{-1}}\)
= 15A/cm\(^{-1}\)
Intercept C on the vertical axis = 0.04A
k = c/s = \(\frac{0.04}{15}\) = 0.00267 = 2.67 x 10\(^{-3}\)
From the graph, when d = 55cm, I = 0.31A
Precautions; I
- ensured that the keys was open after each reading so that the battery did not run down quickly.
- ensured there was zero error when taking the ammeter reading.
- Key was removed when readings were not being taken
- ensured terminals are clean/tight
- Noted and corrected/avoided zero error on ammeter metre rule
(b)i. The potential difference between two points in an electric circuit is the work done (in joules) when one coulomb of electric charge moves from one point to the other
ii. - Nature of wire/resistivity
- Length of wire
- Cross-sectional area of wire/thickness of wire
- Temperature