The correct answer is Option (1) → Mercury cell
The cell traditionally used in hearing aids and other small, low-power electronic devices like watches is the Mercury cell.
Characteristics of the Mercury Cell
- Small Size: Mercury cells are very compact, making them ideal for devices where space is severely limited, like hearing aids.
- Constant Voltage: They maintain a remarkably constant voltage (around 1.35 V) throughout most of their service life, which is critical for consistent performance in sensitive electronics.
- Chemistry: The reaction involves zinc (Zn) as the anode and mercuric oxide (HgO) as the cathode in an alkaline (KOH or NaOH) electrolyte.
$\text{Zn(amalgam)+HgO(s)→ZnO(s)+Hg(l)}$
- Modern Replacement: Due to the environmental toxicity of mercury, modern hearing aids have largely replaced mercury cells with Zinc-air batteries, which are also compact and highly efficient, or rechargeable lithium-ion batteries.
Other Cells (For Comparison)
- Dry Cell (Leclanché): Larger, not suitable for small devices; voltage drops over use.
- Lead Storage Cell: Very large, heavy, and used in automobiles; requires recharge.
- Fuel Cell: Used for large power generation; not a compact battery source.
|
