A student was asked to investigate the variation of current with potential difference for a thin metallic conductor - Leaving Cert Physics - Question 4 - 2013

The device used to vary the potential difference in the circuit is the variable resistor (rheostat) or potential divider.

The student adjusted the variable resistor (rheostat) to change its resistance, which in turn alters the voltage across the conductor. By rotating or moving the slider on the rheostat, different levels of resistance can be set, affecting the potential difference measured and consequently the current flowing through the conductor.

1. Label the x-axis as 'Potential Difference (V)' and the y-axis as 'Current (A)'.
2. Plot the points from the table using the V and I values:
   • (1.0, 0.17)
   • (2.0, 0.34)
   • (3.0, 0.50)
   • (4.0, 0.64)
   • (5.0, 0.77)
   • (6.0, 0.88)
3. Draw a straight line connecting the points, which should be linear from the origin, following Ohm's law.

To find the resistance, use Ohm's law, which states that resistance R can be calculated as R = V/I. From the graph, locate the corresponding potential difference when the current is 0.7 A. The resistance can then be calculated as:

$R = \frac{V}{I}$

Assuming the graph indicates V = 4.5 V when I = 0.7 A, then:

$R = \frac{4.5 V}{0.7 A} = 6.43 \Omega$

The graph is linear, indicating that the current increases proportionally with the potential difference, which is consistent with Ohm's law. This means that the resistance of the conductor remains constant over the range measured, thus confirming that the conductor exhibits ohmic behavior.