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Difference between Primary Cell and Secondary Cell
A cell is an active circuit component that supplies electrical energy to the circuit. A cell stores the energy in the form of chemical energy and converts it into electrical energy when the load is connected across its terminals. Depending on the ability to recharge, the cells are classified into the following two types, viz. −
Primary cell
Secondary cell
Read through this article to find out more about primary cells and secondary cells and how these two types of cells are different from each other.
What is a Primary Cell?
The type of electric cell which produces electrical energy by the action of an irreversible chemical reaction is called a primary cell. Since the primary cell involves the irreversible chemical reaction, therefore it cannot be recharged. Thus, the primary cells are designed to use once and then discarded.
The energy density of a primary cell is high; hence it discharges very slowly. The terminal voltage of the primary cell is very less than the EMF of the cell, it is because the internal resistance of a primary cell is very high that causes a high voltage drop within the cell while current drawn from it. Inside a primary cell, there is no fluid, hence it is also termed as dry cell.
The one major advantage of the primary cell is that its cost is quite low. The primary cells are widely used in remote controls, clocks, toys, etc.
What is a Secondary Cell?
The electric cell which can converter chemical energy into electrical energy and vice-versa is called secondary cell. The secondary cells involve reversible chemical reactions that means while the discharging of the cell the reaction takes place in the forward direction to produce electrical energy and while charging the reaction happens in reverse direction to stores the electrical energy in the form of chemical energy. Therefore, the secondary cells are designed to use repeatedly by recharging them again and again.
In long term, the cost of secondary cells is less than that of the primary cells. However, their initial cost is more than the primary cells. The energy density of the secondary cell is low; hence it discharges very quickly. Although, the EMF and the terminal voltage of a secondary cell is almost equal, it is because it has very low internal resistance that causes a very low voltage drop within the cell while discharging.
Secondary cells are used in laboratories to perform experiments, digital cameras, trimmers and many other electronic devices.
Difference between Primary Cell and Secondary Cell
The following table highlights the major differences between a primary cell and a secondary cell −
| Basis of Difference | Primary Cell | Secondary Cell |
|---|---|---|
| Definition | The type of cell that can only convert the chemical energy into electrical energy is known as primary cell. | The type of cell that can convert chemical energy into electrical energy and vice-versa is called secondary cell. |
| Chemical reaction | Primary cell involves irreversible chemical reaction. | The reversible chemical reaction takes place in a secondary cell. |
| Recharging | Primary cell cannot be recharged, once it discharged completely. | Secondary cell can be recharged many times. |
| Use | Primary cell can be used only once and then discarded. | Secondary cell can be used again and again. |
| Internal resistance | The internal resistance of the primary cells is high. | Secondary cells have low internal resistance. |
| Internal voltage drop | Primary cells have high internal voltage drop. | Secondary cells have low internal voltage drop. |
| Terminal voltage | For a primary cell, the terminal voltage is quite less than the EMF of the cell. | The terminal voltage and EMF of a secondary cell are almost equal. |
| Energy density | Primary cells have high energy density. | The energy density of a secondary cell is low. |
| Discharging rate | Primary cells discharge slowly. | Secondary cells discharge quickly. |
| Current | Primary cells are capable for producing weak currents only. | Secondary cells can produce low as well as high currents. |
| Size and weight | The primary cells are smaller in size and light in weight. | Secondary cells are comparatively larger in size and heavy. |
| Inside content | There is no fluid inside a primary cell, hence it is sometimes called dry cell. | Secondary cell contains wet cell and molten salts inside it. |
| Initial cost | The initial cost of primary cells is low. | The initial cost of a secondary cell is relatively high. |
| Design | The design of primary cell is simple. | The design of secondary cell is complex. |
| Examples | Dry cells, mercury cell and Daniel cell are the common examples of primary cells. | Nickel-cadmium cell, Nickel-iron cell, Lead-acid cell, etc. are the examples of secondary cells. |
| Applications | The primary cells are generally used in clocks, remote controls, torches and many other small sized portable devices. | Secondary cells are used in digital cameras, toys, labs to perform experiments, etc. |
Conclusion
The most significant difference between primary cells and secondary cells is that a primary cell cannot be recharged again, whereas a secondary cell can be recharged many times. Both primary and secondary cells are widely used in many portable devices to power them.
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