The greenish-blue spot will appear around the wire now connected to the positive terminal.
Explanation
The phenomenon described is the chemical effect of electric current. When an electric current flows through a conducting solution (electrolyte), chemical reactions occur at the electrodes. A raw potato contains moisture and dissolved salts, allowing it to act as an electrolyte.
Analysis of the Experiment:
- Mechanism: When copper wires are used as electrodes in a potato, the current causes a chemical reaction at the positive terminal (anode). The copper wire reacts with the electrolyte inside the potato to form a greenish-blue compound (typically copper ions reacting to form salts).
- Polarity Indication: This specific color change is a visual indicator used to identify the positive terminal. It does not occur at the negative terminal (cathode).
- Effect of Reversal: If the polarity of the battery is reversed, the direction of the current changes. The wire that was previously connected to the negative terminal becomes the positive terminal. Consequently, the chemical reaction responsible for the greenish-blue spot will now occur at this new positive wire.
Key Takeaway:
The formation of a greenish-blue spot in a potato experiment is due to the chemical effect of electric current and serves as a definitive test to identify the positive terminal.