A greenish-blue spot appears around the positive electrode.
Explanation
The phenomenon described is a demonstration of the chemical effect of electric current. When electric current passes through a conducting solution or a moist medium containing electrolytes (such as the juices inside a potato), chemical reactions occur at the electrodes.
Detailed Analysis:
- Conductivity of Potato: A raw potato contains moisture and dissolved salts, which act as electrolytes, allowing the conduction of electricity.
- Chemical Reaction at the Positive Terminal: When current flows, a chemical reaction takes place specifically at the electrode connected to the positive terminal. If copper wires are used, the reaction between the copper, the current, and the potato's contents produces a greenish-blue spot around the insertion point.
- Identification of Polarity: This specific color change does not occur at the negative terminal. Therefore, this experiment is frequently used to identify the positive terminal of a concealed battery or cell.
- Other Options: While the passage of current generates some heat (heating effect), the distinct and immediate visual identifier in this context is the chemical color change, not cooking or blackening.
Key Takeaway:
The appearance of a greenish-blue spot on a potato around an electrode signifies the positive terminal, illustrating the chemical effect of electric current.