The principle of this is actually closer to chemistry than to physics, but with a few
easily acquired substances, it is possible to create your own battery. (Actually, to be
more precise, a cell, as a battery is a collection of cells).
But first, a bit of theory behind how it works. When a rod made of a transition metal, such
as copper, is dipped into a solution of its own ions, such as copper sulfate, an
equilibrium is set up between the metal in its solid state and the metal as aqueous ions.
(A certain proportion of the metal atoms exist in the rod as solid atoms and a certain
proportion exist in the solution as aqueous copper 2+ ions).
When some of the metal on the rod dissolves to become aqueous ions, electrons are given up
by the atom (A copper 2+ ion has loses 2 electrons) and build up on the rod giving a
negative electrical charge. This is called a half cell.
The size of the negative charge depends on how good a reducing agent the metal is.
(Reducing agents donate electrons in reactions). So if we take two half cells made of two
different metals and join them together, as one will have a greater negative potential than
the other, a potential difference is set up between the two metal rods. As a potential
difference cause electrons to flow (from the rod with a greater negative charge to the rod
with a smaller negative charge), a cell will have been created.
When a copper half cell and a zinc half cell are joined together, they can generate enough
current to light a bulb and it is the basis of a cell called the Daniell Cell.
Finally, now you know the theory, here's how you actually create a Daniell Cell. (See
Take a copper can filled with copper sulfate solution. Now take a smaller POROUS
pot (so that the moving electrons can pass through), full of a zinc sulphate solution, and
place it inside the copper can. Ensure that the zinc sulphate does not pour over and mix
with the copper sulphate solution. Now place a zinc rod so that it is partially submerged
in the zinc solution. Connect a bulb by one of its terminals to the top end of the zinc rod
with a wire, and finally connect the other terminal of the bulb to the copper can with
another wire. And voila! You have made a Daniell Cell, your very own battery!
Answered by: Simon Hooks, Physics A-Level Student, Gosport, UK
'The mathematician's patterns, like the painter's or the poets, must be beautiful; the ideas, like the colours or the words, must fit together in a harmonious way. Beauty is the first test: there is no permanent place in the world for ugly mathematics.'