What is cells ?
2. The smallest element of a battery is a cell. A cell is defined as a source of emf in which chemical energy is converted into electrical energy.
3. A cell consists of two metal plates of different materials. These plates are immersed in a suitable solution.
The value of emf produced by a cell depends on
1. Material used for the plates or electrodes. 2. Types of electrolytes.
What is Battery ?
1. A battery is a group of cells. Depending on the voltage and current requirements, the cells are suitably connected in series-parallel configurations.
3. The batteries give out electrical energy due to the chemical reactions taking place while discharging.
4. During the charging process, the battery's chemical changes take place, which absorbs the energy.
5. Thus batteries absorb electrical energy at the time of charging and release it at the time of discharging.
6. A battery consists of a number of cells connected in series to deliver the required output voltage.
(say 6V or 12V or 24, 48, 72 volts).
Classification of Cells :
The cells are classified into two categories:
(1) Primary cells and (2) Secondary cells
What is Primary and Secondary cells ?
Primary cells :
1. The chemical action taking place in the primary cells is irreversible. Hence once the terminal voltage goes down, we have to replace the primary cell by a new one.
2. The best example of primary cells is the dry cells available in market which are used for radio, walkman, calculators etc.
3. The energy producing capacity of primary cells is limited.
4. Examples of primary cells are alkaline cell, mercury cell, zinc-chloride cell etc.
Secondary cells :
1. The chemical action taking place in the secondary cells is reversible. So it is possible to recharge the cell if it is in the discharged state.
2. In the charging process we have to pass a charging current through the cell in the opposite direction to that of the discharging current.
3. The electrical energy is stored in the form of chemical form, when the charging current is
passed.
4. Secondary cells are capable of producing a large amount of energy.
5. Examples of secondary cells are lead-acid cells, Nickel cadmium alkalinc cells.
6. The secondary cells are also called as storage cells or rechargeable cells.
7. There are different types of secondary cells. The commonly used ones are :
1. Lead acid cell. 2. Nickel iron alkaline cell. 3. Nickel cadmium-alkaline cell.