Essential Idea:

Electric cells allow us to store energy in a chemical form and then release it as electrical energy to perform work elsewhere.

To make a chemical cell, or a battery, you can begin with a container of weak acid, and two electrodes made of different metals.

• Different metals dissolve in acids at different rates.
• When a metal dissolves, it enters the acid as a positive ion, leaving behind an electron.
• We call the weak acid the electrolyte. We call the least negative metal the positive terminal. We call the most negative metal the negative terminal.

Cells operate as direct-current (dc) devices meaning that the cell drives charge in one direction.

If we connect conductors and a light bulb to the (+) and the (-) terminals, electrons begin to flow in an electric current.

• Each time an electron leaves the (-), the acid creates another electron.
• Each time an electron enters the (+), the acid neutralises the electron.
• This process is maintained until one of the metals or the electrolyte is completely used up.
• A primary cell can’t be recharged.
• A secondary cell can be recharged by applying an external voltage, reversing the chemical reaction.

A simple cell produces a potential difference of about 1 V.

Electromotive Force (again…)

Once connected to a circuit, the battery (cell) provides a potential difference which allows all charges to flow in the same direction. The chemical energy of the battery is eventually converted into thermal energy, into mechanical work and into chemical energy again.

The electrons leave the negative terminal of the cell. They pass around the circuit and re-enter the cell at the positive terminal.

In the cell, negative ions are pushed from the negative to the positive terminal and positive ions in the opposite direction.