Polarization:
The hydrogen bubbles which are clinging over the surface of copper electrode (anode) becomes a thin film of hydrogen over the copper electrode. This hydrogen film increases the internal resistance and reduces the emf of the cell and hence the cell soon becomes inactive. This effect is known as polarization.
Local action:
In voltaic cell it is observed that, when the cell is not connected to the load and not supplying any current zinc will continuously dissolving in the electrolyte. This is due to the impurities (copper, iron, tin, and lead) in the commercial zinc. So that whenever commercial zinc is used as a electrode, separate small cells are developed between the impurities and zinc with the presence of electrolyte. These local cells consume always zinc and the emf developed by those local cells are always opposite to the main emf. The action of these cells is known as local action.
