Question

Distinguish between primary and secondary cells.

Answer 1

Hint: Recall that a cell converts chemical energy to electrical energy. We know that primary cells are cheap and simple in design whereas secondary cells are relatively expensive and complex in design. In such a case, determine what makes them simple or complex in terms of their structure and rechargeability. To this end, establish a distinction between them with respect to their applications.

Complete Solution:
Let us begin by understanding what electric cells basically are.
Any device that is capable of converting chemical energy into electrical energy and is used to generate electricity via chemical reactions is called an electric cell. It essentially serves as a power supply unit that converts stored chemical energy into electrical potential energy which allows a current to flow from the positive terminal to the negative terminal of an external circuit.

Now let us look at the two types of cells.
Primary cells are non-rechargeable cells whose chemical reaction is irreversible. They have a very high internal resistance and high energy density so they discharge very slowly. They do not contain any fluid and are called dry cells. They are usually lightweight and inexpensive and easy to use. When current is drawn from a primary cell, chemical energy is converted to electrical energy. The alkaline batteries that we use around our household is an example of primary cells.

Secondary cells are rechargeable cells whose chemical reactions are reversible. They have a low internal resistance and a smaller energy density so they discharge relatively quicker. They are made up of molten salts and are called wet cells. They are usually heavier and relatively expensive and have a complex design. Like primary cells, they convert chemical energy to electrical energy when current is drawn from it. But when current is supplied, they convert the electrical energy to chemical energy, which is how they are recharged. The Lithium-ion battery is an example of secondary cells.

Primary cells as one-time use and disposable, whereas secondary cells can be used multiple times by recharging them.

Note:
Do not get confused between a cell and a battery.

A cell is a single device that produces electrical energy but a battery usually consists of a group of cells. A cell supplies power for a shorter period of time while a battery can supply power for long durations. Cells can either be dry or wet types, whereas batteries are either rechargeable or non-rechargeable. A cell typically generates energy from chemical reactions whereas a battery essentially just stores energy. A cell is used for less intense tasks such as in alarm clocks, lamps, etc., whereas batteries are used in heavy-duty applications such as inverters, automobiles, and so on.