How do primary and secondary cells differ?

Primary cells are single-use and cannot be recharged, while secondary cells are rechargeable and can be used multiple times.

Primary and secondary cells are two types of electrochemical cells that are used to generate electrical energy. The main difference between them lies in their reusability. Primary cells, also known as disposable batteries, are designed to be used once and discarded. They cannot be recharged once the chemical reactions that produce the electrical energy are complete. Examples of primary cells include alkaline batteries and button cells.

Secondary cells, on the other hand, are designed to be recharged and used multiple times. The chemical reactions that occur within these cells are reversible, allowing the cell to be recharged once the energy has been depleted. This is achieved by applying an external electrical power source, which drives the reaction in the opposite direction, restoring the cell's charge. Examples of secondary cells include lead-acid batteries (like those used in cars) and lithium-ion batteries (like those in your mobile phone or laptop).

For a more detailed understanding of the chemical reactions in cells, consider reading about chemical cells.

The operation of both primary and secondary cells is based on the same fundamental principle: a redox reaction. In a redox reaction, one substance is reduced (gains electrons) and another is oxidised (loses electrons). This movement of electrons from the oxidised substance to the reduced substance can be harnessed to do electrical work.

In primary cells, the materials that make up the anode and cathode are chosen such that the redox reaction is energetically favourable and occurs spontaneously once the circuit is closed. However, once the reactants are exhausted, the reaction cannot be reversed, and the cell is spent.

In secondary cells, the materials are chosen such that the redox reaction can be driven in reverse by applying an external voltage. This recharges the cell, allowing it to be used again. However, each time the cell is charged and discharged, there is some degradation of the cell components, which over time reduces the cell's capacity. Understanding the equipotential surfaces can further elucidate the energy distribution within these cells.

IB Physics Tutor Summary: Primary cells are used once and then discarded because their chemical reactions can't be reversed. Secondary cells, like those in phones and cars, can be recharged multiple times as their reactions are reversible. Both work through redox reactions, where substances gain or lose electrons. However, secondary cells can degrade over time with repeated charging and discharging.

Additionally, understanding the principles of resistivity and conductivity can provide insights into how different materials within the cells affect their efficiency and performance.