Friday, May 31

Ordinary Dry Cell

Introduction to ordinary dry cell:

The best known voltaic cell for commercial use is the ordinary dry cell. The dry cell which we use in torches, transistor radios, toys and laboratory experiments, was invented by Lechlanche in 1868. The dry cell converts chemical energy into electric energy. A single dry cell gives a voltage of 1.5 volts.

Construction of ordinary dry cell

A dry cell consists of a carbon rod placed at the centre of a zinc container. The space between the carbon rod and the zinc container is filled with a moist paste of ammonium chloride (NH4Cl) and zinc chloride (ZnCl2) mixed with manganese dioxide and powdered carbon. In dry cell, the carbon rod acts as a positive electrode (cathode); the zinc container act as a negative electrode (anode); and the ammonium chloride and zinc chloride acts as electrolyte. Manganese dioxide removes the hydrogen gas formed during the working of dry cell (by oxidising it), and prevent it settling on the positive electrode of the cell (so that it may not interfere with the working of the cell).

How ordinary dry cell works:

Actually, manganese dioxide works as depolariser (depolariser is a chemical which removes hydrogen and prevent it settling on the positive elctrode of the cell). powdered Carbon present in the dry cell helps in the movement of charges between the electrodes in the cell and hence reduces the internal resistance of the cell. Please note that a dry cell is not completely dry. The presence of little water in the miost paste is essential for the movement of ions.The dry cell is sealed at the top with the sealing wax to prevent evaporation of moisture and the carbon rod has a brass cap for better electrical contact. The zinc container has an outer insulation of card board case. The card board case, however does not cover the bottom of the cell. In dry cell , the zinc container is the producer of electrons for the usable current.

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