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 power supply unit (p.s.u.) which varied the voltage applied across the electrolyte. This adjustment allowed for different voltage readings and thus different corresponding current values.

The graph should have the voltage (V) on the x-axis and the current (I) on the y-axis. Each point representing voltage from the table should be plotted against its corresponding current. Ensure the following:

• Label the axes correctly on graph paper.
• Plot all six points accurately.
• Draw a straight line that best fits the data points indicating a direct relationship.
• Ensure good distribution of points without clustering.

To find the resistance (R) of the electrolyte, use the formula derived from Ohm's law, where resistance is equal to voltage divided by current:

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

Using data from the graph, calculate the slope:

• Take two points, for example, (2, 64) and (6, 195), the change in voltage is 6 - 2 = 4 V, and the change in current is 195 - 64 = 131 mA.
• Hence, the resistance is given by:

$R = \frac{4}{0.131} \approx 30.96 \Omega$

In simplified form, this equals approximately 31 Ω.

As current flowed through the electrolyte, the cathode (negative electrode) became heavier as it was coated with fresh copper from the electrolyte solution, while the anode (positive electrode) got lighter due to the oxidation of copper ions. The visual change includes a color shift in the electrolyte, indicating the movement and deposition of copper.