Why do electric cells have different voltages?

Electric cells have different voltages due to the varying chemical reactions occurring within them.

The voltage, or electromotive force (EMF), of an electric cell is determined by the specific chemical reaction that takes place within it. This reaction involves the movement of electrons from one substance to another, a process known as redox (reduction-oxidation) reaction. Different substances have different tendencies to lose or gain electrons, a property known as electrode potential. The difference in electrode potentials of the two substances involved in the reaction gives rise to the cell's voltage.

For instance, in a standard alkaline cell, the reaction between zinc and manganese dioxide generates a voltage of about 1.5 volts. In contrast, a lithium-ion cell, which involves a reaction between lithium and cobalt oxide, can produce a voltage of around 3.7 volts. The specific substances used, and the way they are combined, can therefore significantly affect the voltage produced by a cell.

Moreover, the design of the cell also plays a role in determining its voltage. For example, in a series connection, the voltages of individual cells are added up, resulting in a higher total voltage. On the other hand, in a parallel connection, the voltage remains the same as that of a single cell, but the capacity or total available charge is increased.

In summary, the voltage of an electric cell is primarily determined by the chemical reaction taking place within it, which is influenced by the specific substances used and their electrode potentials. The design of the cell can also affect its voltage, particularly when multiple cells are combined. Understanding these factors can help in selecting the appropriate cell for a particular application, whether it's powering a small electronic device or an electric vehicle.