Question 1
AIM: To verify the relationship between current and voltage at constant resistance.
- (a)Connect the circuit diagram as shown in figure 1.
- (b)Ask the supervisor to check the circuit connection.
- (c)Copy Table 1 in the answer booklet.
Table 1
Voltage(V) |
Current (A) |
Resistance (W) = V/I |
0 |
|
|
2 |
|
|
4 |
|
|
6 |
|
|
8 |
|
|
10 |
|
|
- (d)Switch on the variac.
- (e)Set the variac to 0V
- (f)Read and record the ammeter readings in Table 1.
- (g) Increase the variac voltage in steps of 2V up to 10V and record the corresponding ammeter readings in Table 1.
- (h)Switch off the variac.
- (i)Complete Table 1.
- (j)Plot a graph of voltage (V) on the vertical axis against current (A) on the horizontal axis.
- (k)Determine the slope of the graph.
- Comment on the graph.
Observation
The expected answers were:
(a)
Table 1
Source voltage (V) |
Ammeter reading |
Voltmeter reading |
0 |
0.00 |
0.00 |
2 |
138.12 |
1.99 |
4 |
276.23 |
3.97 |
6 |
414.35 |
5.96 |
8 |
552.47 |
7.95 |
10 |
690.58 |
9.94 |
(b) Correct reading of both ammeter and voltmeter
(c) Correct axes (x,y and origin)
(d) Reasonable scale and title
(e) Plotting of points
(f) Line of best fit (one having scattered points very well
(g) Slope of graph (A linear graph)
(h) Relationship obeys Ohm's law
Candidates were required to determine the relationship between current and voltage in a series circuit.
The candidates, as reported, understood the question and carried out the task required. But some of the candidates did not record accurate voltage and current readings.