Name the cell used in hearing aids. Write the cell reaction. Why do they give consistent supply of current at a low potential?

Dear student,


The cell used in hearing aids is Mercury cell . In this cell anode is Zn- Hg amalgam and cathode is the paste of HgO and C .
The cell reactions are : 
   At anode :   Zn (amalgam)  +  2 OH^-   $\to$  ZnO _(s)  + H₂O   + 2e^-
   At cathode :  HgO_(s)  + H₂O + 2e^-   $\to$  Hg_(l)  + 2OH^-
Over all reaction :  Zn   +  HgO   $\to$  ZnO   +  Hg
Since the over all reaction does not involve any ion in solution whose concentration can change, the cell showes a consistance supply of current .
  Regards