TEST OF PRACTICAL KNOWLEDGE QUESTION You are provided with a variable d.c. power supply E, a \(2\propto\) standard resistor, a key, an ammeter, a voltmeter ...
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.
(a) Table of readings
For each value of \(E\) the voltmeter reading \(V\) and the corresponding ammeter reading \(I\) are recorded, and the reciprocals \(V^{-1}\) and \(I^{-1}\) are evaluated:
S/N
\(E\)/V
\(I\)/A
\(V\)/V
\(V^{-1}\)/V\(^{-1}\)
\(I^{-1}\)/A\(^{-1}\)
1
1.5
0.30
0.80
1.250
3.333
2
3.0
0.50
1.40
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
(viii) Graph of \(V^{-1}\) against \(I^{-1}\)
\(V^{-1}\) is plotted on the vertical axis and \(I^{-1}\) on the horizontal axis, both axes starting from the origin \((0,0)\). A best straight line is drawn through the plotted points:
V^{-1} (vertical) plotted against I^{-1} (horizontal), both axes from the origin; slope s \u2248 2.6, vertical-axis intercept e \u2248 0.04.
(ix) Slope of the graph
Two widely-separated points are read off the best line, \((I^{-1}_1, V^{-1}_1) = (0.26,\ 0.800)\) and \((I^{-1}_2, V^{-1}_2) = (1.24,\ 3.333)\):
Where the best line meets the \(V^{-1}\) axis (at \(I^{-1} = 0\)):
\[ e \approx 0.04\ \text{V}^{-1}. \]
(xi) Two precautions
Ensured all terminals were clean and every connection was tight, and checked for and corrected any zero error on the voltmeter and ammeter.
Opened the key immediately after each pair of readings was taken to avoid heating the resistor and running down the cell, and read both meters with the eye directly in line with the pointer to avoid parallax error.
(b)(i) Two methods of producing an electric current
Chemical action in cells, accumulators or fuel cells (chemical energy converted to electrical energy).
Electromagnetic induction using a generator or dynamo (mechanical energy converted to electrical energy). Solar/photocells and thermocouples are also acceptable.
(b)(ii) Value of \(R\)
The two resistors \(R\) are connected in parallel:
This parallel combination is in series with the \(2\ \Omega\) standard resistor, and the effective (total) resistance of the circuit is \(4.0\ \Omega\) with negligible internal resistance:
For each value of \(E\) the voltmeter reading \(V\) and the corresponding ammeter reading \(I\) are recorded, and the reciprocals \(V^{-1}\) and \(I^{-1}\) are evaluated:
S/N
\(E\)/V
\(I\)/A
\(V\)/V
\(V^{-1}\)/V\(^{-1}\)
\(I^{-1}\)/A\(^{-1}\)
1
1.5
0.30
0.80
1.250
3.333
2
3.0
0.50
1.40
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
(viii) Graph of \(V^{-1}\) against \(I^{-1}\)
\(V^{-1}\) is plotted on the vertical axis and \(I^{-1}\) on the horizontal axis, both axes starting from the origin \((0,0)\). A best straight line is drawn through the plotted points:
V^{-1} (vertical) plotted against I^{-1} (horizontal), both axes from the origin; slope s \u2248 2.6, vertical-axis intercept e \u2248 0.04.
(ix) Slope of the graph
Two widely-separated points are read off the best line, \((I^{-1}_1, V^{-1}_1) = (0.26,\ 0.800)\) and \((I^{-1}_2, V^{-1}_2) = (1.24,\ 3.333)\):
Where the best line meets the \(V^{-1}\) axis (at \(I^{-1} = 0\)):
\[ e \approx 0.04\ \text{V}^{-1}. \]
(xi) Two precautions
Ensured all terminals were clean and every connection was tight, and checked for and corrected any zero error on the voltmeter and ammeter.
Opened the key immediately after each pair of readings was taken to avoid heating the resistor and running down the cell, and read both meters with the eye directly in line with the pointer to avoid parallax error.
(b)(i) Two methods of producing an electric current
Chemical action in cells, accumulators or fuel cells (chemical energy converted to electrical energy).
Electromagnetic induction using a generator or dynamo (mechanical energy converted to electrical energy). Solar/photocells and thermocouples are also acceptable.
(b)(ii) Value of \(R\)
The two resistors \(R\) are connected in parallel:
This parallel combination is in series with the \(2\ \Omega\) standard resistor, and the effective (total) resistance of the circuit is \(4.0\ \Omega\) with negligible internal resistance:
