Cells and Batteries
Cells and batteries supply current which always passes in the same direction and are thus sources of direct current.
The underlying principle of operation in a battery is an ELECTROCHEMICAL REACTION i.e. a chemical reaction that produces electrons. In a battery electrons are made to move in one direction by lining up different types of metals/materials. The principle behind the selection of metal is to choose one with a lot of free electrons and the other requiring free electrons. The electrons are produced by the chemical reaction between the electrolyte and metal.
Below is an explanation of the battery reaction:
The Sulphuric Acid reacts with the Zinc electrode. As a result the acid molecule breaks up into 2H+ and one SO42- ions.
The Zinc atoms on the surface of the Zinc rod go to
Zn ————→ Zn2+ + 2e-
The Zn2+ combines with the SO42-
Zn2+ + SO42- ————→ ZnSO4which dissolves in the acid.
The excess electrons flow through the wire and load to the Carbon electrode as this is the easier route.
The electrons combine with the hydrogen on the carbon rod releasing hydrogen gas.
2H+ + 2e- ————→ H2 gas
The above only happens when the circuit is complete
Solar cells are also known as photovoltaic cells as they transfer energy from light photons (sunlight) to electrical energy.