Simple Method of Producing Electricity
Current may be produced in cells known as batteries, or it may
be produced by cutting the magnetic lines of force between opposite poles of a
magnet. The first method is chemical and was discovered by Volta in 1800. A jar filled with dilute sulfuric acid into
which we place a strip of zinc and a strip of copper, the two strips being
connected by a copper wire.
A chemical reaction takes place and a current is set up which
flows through the wire in the direction from the copper to the zinc. If the
terminals of an electric bell or a small electric lamp are interposed between
two parts of this wire, the bell will ring or the light will light.
The poles of a battery
are called the electrodes copper being the positive electrode and zinc
being the negative electrode. The battery just described is also known as a wet
cell battery. A dry cell battery works on the same principle although different
chemicals are used.
By hooking up
several dry cell batteries, the positive pole of one connecting with the
negative pole of the next one, and so on in a series, we can develop more and
more electromotive force, since the total voltage will be the sum total of the
separate voltages developed by each individual battery.
Construction of the old
dry cell model
Dry cells are used almost exclusively in common electrical
devices such as bells, flashlights, signal devices, etc. The negative pole is the
outside zinc can which serves as a containing vessel. The positive pole is a
cylinder of carbon or a carbon rod.
Instead of sulfuric acid being used to develop the current between
the zinc and the carbon, the space between the zinc and the carbon is filled
with granulated carbon and manganese dioxide soaked in ammonium chloride.
These chemicals react to set up an electric current that
flows from the positive carbon pole to the outside of the zinc which acts as
the negative pole. The cell is sealed with pitch at eh top and contains cardboard
and blotting paper around the sides, which reinforces it and makes a compact
unit.
In some cells, copper is substituted for carbon, as you will
see if you examine a flashlight battery. When the cell is put into the
flashlight holder the small electric bulb is in contact with the outside zinc. By
pressing a small lever at the top of the casing of the flashlight, the zinc of
the cell contact with the bulb. The bulb is therefore brought in contact with both
copper and zinc, the circuit is closed, and the bulb lights.
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