Generation of electricity
Electricity can be generated in 6 basic ways. These are by:
Magnetism and Motion.
We shall look at these methods briefly.
Chemical Action (Cell)
This is by use of 2 different metals placed in a liquid called an
electrolyte. We call this a cell and by grouping these cells we
produce a battery.
Friction (Static Electricity)
When a comb is passed through hair it acquires an electrical charge.
If a piece of tissue paper is then held close to the comb it is attracted
towards it. These effects are due to static electricity (electrostatics).
Aircraft in flight build up large amounts of static electricity and acquire
a charge potential much greater than that of the atmosphere. This
charging of the aircraft is undesirable but unavoidable, although the
effects can be minimized.
Pressure (Crystal Controlled Oscillators)
Certain crystalline substances, notably quartz, exhibit a piezoelectric
effect which results in PD appearing between the opposite faces of
the crystal when it is mechanically deformed and vice versa. The
Crystal can be shown to
Light (Photovoltaic Cells)
These devices utilize the energy from a light source to produce
These devices can be used power battery chargers when connected
as solar panels.
At the point of contact between 2 different metals there exists an
electrical potential difference, which depends on the temperature of
the junction. When we complete the circuit with a second junction at
a different temperature, a current flows in the circuit.
This thermoelectric effect is called the Seebeck effect after the man
who discovered it, and the junction is called a ‘thermocouple’. Either
the net EMF in the circuit or the resulting current may be used to
Primary cells are called so, as the chemical reaction used to
produce the output voltage is extremely difficult, or impossible to
reverse i.e. they cannot be recharged, an example of this is the dry
primary cell, a standard type of dry primary cell is the Zinc carbon
cell, these are constructed by having 2 poles, one of them being a
carbon rod which is the + ve (cathode) and the other pole being
made of zinc, this being the –ve (anode) connected to a steel disc at
the bottom of the cell to aid connection to a circuit. In a dry cell the
zinc pole also acts as the container and surrounds the carbon rod,
and also holds the electrolyte, which is constructed from ammonium
chloride (sal-ammoniac). With this basic arrangement there is a
very distinct disadvantage in that as the cell is being discharged the
chemical reaction that takes place produces hydrogen bubbles
which accumulate around the carbon rod and effectively insulate it
from the electrolyte. To overcome this reaction – known as
polarisation, manganese dioxide is added to the electrolyte during
construction, Another problem that occurs in a dry primary cell is
that because the case is made of zinc this has a tendency to
corrode rapidly, this leads to the case leaking the electrolyte that it is
holding, to prevent this the electrolyte is mixed with wheat flour so
that it forms a thick paste and hence the term “dry” cell. The EMF of
a dry cell is approximately 1.5 volts.