Question

Which cell gives a constant voltage throughout its life and why?

Answer 1

1. The mercury cell is a cell that gives constant voltage throughout its life. It is an electrochemical battery and is non-rechargeable.
2. The electrodes of the battery are made up of zinc and mercuric oxide respectively. The zinc gets oxidized to zinc oxide (electron loss) and the mercuric oxide gets reduced to mercury (electron gain).
3. There is no involvement of ions like in other batteries and the generation of voltage is dependent entirely on the process of oxidation and reduction of the respective electrodes. So, as long as the electrodes are completely or nearly used up, the potential difference generated will be roughly constant.

Hence, the potential difference produced by the mercury cells remains nearly the same throughout its lifetime.