Primary Cells

There are three types of primary cells - the simple cell, the Daniel cell and the Leclanché cell.

Simple Cell:

Simple cells consist of a copper and zinc electrodeElectrodes are conductors, in the form of wires, rods or plates, through which current enters and leaves the electrolyte. When the current leaves the electrodes it is known as the cathode... More (metal plate) dipped in dilute sulphuric acid (tetraoxosulphate(VI) acid) contained in a glass vessel. The copper plate is positive and the zinc plate is negative. When the pure zinc plate and the copper plate are joined together by a wire, the zinc begins to dissolve and bubbles of hydrogen are formed on the copper plate. A small electric bulb connected to the wire lights up showing that current is flowing in the wire. A voltmeter shows that the copper plate is at a higher potential than the zinc plate.

Defects of a Simple Cell:

Polarization:

This is the production of hydrogen bubbles at the surface of the copper plate. These bubbles weaken the current by insulating copper plate leading to a large increase in the resistance between the plates of the cell.

They also produce back e.m.f in the cell that opposes the othe forward emf of the cell generated between