A student investigated the variation of the current I through an electrolyte as the potential difference V across the electrolyte was changed - Leaving Cert Physics - Question 4 - 2011

The potential difference was changed by adjusting the dial or selector on the variable power supply unit (p.s.u.). This allowed the investigator to systematically increase the voltage applied across the electrolyte.

Plot the current (I in mA) on the y-axis against the potential difference (V in V) on the x-axis. Ensure the following:

1. Axes are labeled correctly.
2. Plot six data points from the provided table:
   • (0, 0), (1, 30), (2, 64), (3, 93), (4, 122), (5, 160), (6, 195).
3. Draw a straight line through the points, indicating a linear relationship.

Using the slope method for resistance calculation:

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

From the graph, if we calculate the slope:

1. Take two points from the line, e.g., (1, 30) and (6, 195).
2. Calculate the slope:
   • Change in Voltage (ΔV) = 6 - 1 = 5 V
   • Change in Current (ΔI) = 195 - 30 = 165 mA
   • Slope = $\frac{ΔV}{ΔI} = \frac{5}{165}$

Then, rearranging gives:

$R = \frac{5}{0.165} \approx 30.96 \Omega$

At the electrodes, the following observations were made:

1. Anode: The electrode became lighter due to the oxidation of copper ions, which dissolve into the solution.
2. Cathode: The electrode was observed to be coated with fresh copper as copper ions in the solution gain electrons and reduce to solid copper on the cathode surface.
3. Additionally, changes in the color intensity of the electrolyte may be observed as copper ions are deposited.