The
discovery
of
electricity
How electricity is used
Electricity is especially important because it can be
easily changed to other forms of energy. It can be
changed into heat, light, chemical and mechanical
energy. These forms of energy can then be used for
many purposes.
1
The discovery of electricity fact
sheets reviewed and updated with
the assistance of STAV Publishing
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friendly
2
Heat energy
Electricity heats all wires it flows through, but normally the heat is so
little that the wires feel cold. The more electricity that flows in a given
size wire, the greater the heat generated.
RESISTANCE WIRE
CERAMIC TUBE
Some types of wires get hotter than others because electricity finds
it hard to flow through them. These are called resistance wires. If a
resistance wire and a copper wire — electricity flows easily through
copper — of the same thickness were joined together end to end, and
enough electricity was passed through them, the resistance wire would
get very hot and the copper wire hardly warm.
The thicker the wire, of any given material, the easier it is for electricity
to flow. A thin wire will get hotter than a thick wire if both are joined
together and electricity passes through them.
In some domestic and industrial appliances, a special high resistance
wire which is able to operate in air, at high temperatures for a long
time without deterioration, is used. Examples are toaster and radiator
elements.
As there is no combustion with electricity, heat energy can be used
in enclosed spaces like the inside of an iron or electric jug. This is
considered a most efficient way of heating as there are no heat losses
such as are incurred in maintaining combustion, or an open flame.
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STIRRER
WAVE GUIDE
Microwave oven
Microwave ovens use a magnetron to produce high frequency
electromagnetic waves inside an oven.
MAGNETRON
GLASS PLATE
When microwaves meet something in their path various things happen.
They pass through materials like glass and china without heating them
and are reflected by metal surfaces. The waves are absorbed by other
substances such as food. When this happens, the molecules in the
food are agitated causing a generation of heat which warms or cooks
the food.
Induction cooktop
CERAMIC TOP
(COLD)
MAGNETIC
FIELD
INDUCTION
COIL
Another energy efficient development is the induction cooktop.
Electrical energy is transferred directly into the cooking vessel by a
rapidly changing magnetic field which is created by the electronic
induction generator placed beneath the ceramic cooking top.
If the cooking vessel is ferrous (i.e. steel, cast iron or magnetic stainless
steel), a considerable transfer of energy takes place immediately by
converting the induced current in the cooking vessel to heat.
ELECTRONIC GENERATOR
POWER SUPPLY
3
In effect, the cooking receptacle itself becomes the heating element.
The ceramic top only gets warm (immediately under the container) due
to heat conducted back from the saucepan. It is not heated by the
magnetic field. The result is direct heat transfer to the food, without the
energy waste which occurs when conventional hotplates and boiling
tops are used.
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4
<Electrochemistry
Activity>
How electricity is used in chemistry
If an electrical current is passed from one metal plate to another
through an acid liquid, tiny particles of metal are taken off one metal
plate (called the positive connection or “anode’) and, after being
carried through the liquid, are deposited on the other metal plate
(called the negative connection or “cathode’).
To protect a metal (such as iron or steel) from rusting, or to provide a
surface capable of being highly polished, electricity is used to deposit
a thin layer of some other metal which will not rust (such as nickel) on
the first metal. The chemical action of an electric current used in this
way is called “electro-plating”.
A bicycle handlebar – an example
COPPER PLATE
(ANODE +)
A bicycle handlebar of steel is firstly electro-plated
with copper in a “bath” such as copper sulphate liquid.
A piece of copper is used as the anode, and particles
of this copper are deposited on the handlebar which
is used as the cathode. Nickel is deposited on the
handlebar over the copper-plating, and the handlebar
is then polished.
A process of decomposing chemical compounds
with an electric current (called electrolysis) is used
for the large scale production of sodium, chlorine,
sodium hydroxide, hydrogen, oxygen and zinc. It is
also used for purifying of copper, gold and other similar
substances.
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BICYCLE
HANDLEBAR
(CATHODE -)
CONDUCTING LIQUID,
COPPER SULPHATE
ACID SOLUTION
BATTERY
5
Light energy
Light is a form of energy. The simplest method of converting electrical
energy to light energy is with a filament lamp.
In a filament lamp, a special high resistance wire (filament) is heated by
a current to about 2,600 degrees Celsius. At this temperature, it is white
hot or “incandescent’. Tungsten is used for the filament because it can be
drawn into very thin wires and does not melt at the high temperature. It
would actually burn if exposed to air while white hot and so the air in the
glass globe is replaced by Argon gas, which will not support combustion.
The modern lamp filament is a coil or coiled coil. This reduces the cooling
effect of the surrounding gas and the same current will then maintain
a higher temperature which in turn increases the light output. Coiling,
therefore, improves the efficiency of the lamp, so it gives more light for the
same electricity consumption. The incandescent filament of a lamp is very
bright and if you look directly at it, especially at short range, the glare can
hurt your eyes.
That is why it is important to use properly designed light fittings with
diffusing material which spreads the light, but shields the filament from view.
Luminescent lighting
Electricity flows through metals and it will also flow through gases and
vapours under some conditions. If special gases or vapours are enclosed
in a glass tube and the voltage and gas pressure, together with other
factors, are correctly chosen, a current can be passed through the tube
which causes the gas to become luminous.
This principle is used in neon signs, mercury and sodium street lamps and
fluorescent tubes. Gases and vapours glow with characteristic colours:
for example, neon gas gives red light; mercury vapour- bluish green; and
sodium vapour-yellow.
In the fluorescent lamp, for example, mercury vapour is used. When
current is passed through this vapour, ultra-violet energy is produced.
A fluorescent powder coating which has been placed on the inside of the
tube wall absorbs the ultra-violet energy and, in turn, glows and gives off
visible light. Different fluorescent powders give different colours and with a
suitable mixture, daylight or white light, can be produced.
In either incandescent or luminescent lamps, only a portion of the electrical
energy is turned into light energy. The remainder is converted into heat
energy and is not available for the production of light. Luminescent lamps
change a greater proportion of electrical energy into light energy than
incandescent lamps. That means they consume less electricity for the same
amount of light produced. Luminescent lamps are however more costly and
the fittings are more complicated.
The majority of street lights are controlled by light sensing cells.
These cells automatically switch lights on as daylight fades in the
evening and off as daylight increases in the morning. The cells are
designed in such a way that if one is defective; it causes the lights it
controls to remain switched on. This avoids having areas left without
lighting at night.
Mechanical energy
If a current passes through a conductor which lies in a magnetic
field, there will be relative motion between the conductor and the
field. This is the principle on which the electric motor works.
This is the reverse of the <principle of generator operation>.
The electric motor takes in electrical energy and gives out
mechanical energy as rotary motion. The motor is used to turn
the wheels of industry, drive trams, or operate vacuum cleaners
and refrigerators and many other labour-saving devices in our own
homes. This is another example of how energy may be changed
from one form into another.
Electricity has allowed people to enjoy a higher standard of living
with more goods available and more time for recreation.
6
Electrochemistry Activity
The principles of electrochemistry were first used to protect the hulls of
ships as far back as 1830. Although scientists didn’t understand exactly how
it worked, they noticed that when certain metals were in contact, one metal
would corrode very fast, while the other remained unchanged. Ships were
soon using sacrificial anodes to protect their hulls.
Find out! What are sacrificial anodes? What is the
electrochemistry involved with sacrificial anodes?
•
Prepare a poster or powerpoint presentation showing how
sacrificial anodes and electrochemistry are now used to
protect ships and other metal structures.
Experiment
You will need:
• A small silver object
(jewellery, spoon, coin)
• 150 ml CuSO4
• Strip of copper wire,
1 x 7 cm
• 250 mL beaker
• Emery paper or steel wool
Many industries use electrochemistry to separate metals from metal
ores and put protective metal coatings onto other materials. This
experiment will show you how it can be done on a small scale.
To do
Rub the silver object and the copper strip with emery paper
1.
until each object is shiny.
2.
Place about 150 mL of copper sulfate solution into the beaker.
3.
Put the copper strip and the silver object into the copper
sulfate solution and connect the copper strip to the positive
terminal of the battery and the silver object to the negative
terminal. Make sure the copper and silver objects do not
touch!
4.
Observe the objects every 2 minutes for 15 minutes,
then remove and examine the objects and the solution.
• 6 Volt battery or powerpack
• Clip leads
7
What’s going on?
•
•
Find out more!
•
•
Activity written by Michaela Patel
on behalf of STAV Publishing.
What did you observe in this experiment?
How do you explain your observations?
Which Australian industries use electrochemistry?
What products do you use that have been electroplated?
How electricity is used
Electricity is especially important
because it can be easily changed
to other forms of energy. It can be
changed into heat, light, chemical
and mechanical energy. These forms
of energy can then be used for many
purposes.
Heat energy
Electricity heats all wires it flows through,
but normally the heat is so little that the
wires feel cold. The more electricity that
flows in a given size wire, the greater the
heat generated.
Some types of wires get hotter than others
because electricity finds it hard to flow
through them. These are called resistance
wires. If a resistance wire and a copper wire
— electricity flows easily through copper
— of the same thickness were joined
together end to end, and enough electricity
was passed through them, the resistance
wire would get very hot and the copper wire
hardly warm.
The thicker the wire, of any given material,
the easier it is for electricity to flow. A thin
wire will get hotter than a thick wire if both
are joined together and electricity passes
through them.
In some domestic and industrial appliances,
a special high resistance wire which is able
to operate in air, at high temperatures for
a long time without deterioration, is used.
Examples are toaster and radiator elements.
As there is no combustion with electricity,
heat energy can be used in enclosed
spaces like the inside of an iron or electric
jug. This is considered a most efficient way
of heating as there are no heat losses such
as are incurred in maintaining combustion,
or an open flame.
Microwave oven
Microwave ovens use a magnetron to
produce high frequency electromagnetic
waves inside an oven.
When microwaves meet something in their
path various things happen. They pass
through materials like glass and china
without heating them and are reflected by
metal surfaces. The waves are absorbed
by other substances such as food. When
this happens, the molecules in the food are
agitated causing a generation of heat which
warms or cooks the food.
Induction cooktop
Another energy efficient development is
the induction cooktop. Electrical energy is
transferred directly into the cooking vessel
by a rapidly changing magnetic field which
is created by the electronic induction
generator placed beneath the ceramic
cooking top.
If the cooking vessel is ferrous (i.e. steel,
cast iron or magnetic stainless steel), a
considerable transfer of energy takes place
immediately by converting the induced
current in the cooking vessel to heat.
In effect, the cooking receptacle itself
becomes the heating element. The ceramic
top only gets warm (immediately under the
container) due to heat conducted back
from the saucepan. It is not heated by the
magnetic field. The result is direct heat
transfer to the food, without the energy
waste which occurs when conventional
hotplates and boiling tops are used.
How electricity is used in
chemistry
If an electrical current is passed from one
metal plate to another through an acid
liquid, tiny particles of metal are taken
off one metal plate (called the positive
connection or “anode’) and, after being
carried through the liquid, are deposited on
the other metal plate (called the negative
connection or “cathode’).
To protect a metal (such as iron or steel)
from rusting, or to provide a surface capable
of being highly polished, electricity is used
to deposit a thin layer of some other metal
which will not rust (such as nickel) on the
first metal. The chemical action of an electric
current used in this way is called “electroplating”.
A bicycle handlebar – an example
A bicycle handlebar of steel is firstly electroplated with copper in a “bath” such as
copper sulphate liquid. A piece of copper
is used as the anode, and particles of this
copper are deposited on the handlebar
which is used as the cathode. Nickel
is deposited on the handlebar over the
copper-plating, and the handlebar
is then polished.
A process of decomposing chemical
compounds with an electric current (called
electrolysis) is used for the large scale
production of sodium, chlorine, sodium
hydroxide, hydrogen, oxygen and zinc. It is
also used for purifying of copper, gold and
other similar substances.
The discovery of electricity
fact sheets reviewed and
updated with the assistance
of STAV Publishing
Light energy
Light is a form of energy. The simplest
method of converting electrical energy to
light energy is with a filament lamp.
In a filament lamp, a special high
resistance wire (filament) is heated by a
current to about 2,600 degrees Celsius.
At this temperature, it is white hot or
“incandescent’. Tungsten is used for the
filament because it can be drawn into
very thin wires and does not melt at the
high temperature. It would actually burn if
exposed to air while white hot and so the air
in the glass globe is replaced by Argon gas,
which will not support combustion.
The modern lamp filament is a coil or coiled
coil. This reduces the cooling effect of the
surrounding gas and the same current will
then maintain a higher temperature which
in turn increases the light output. Coiling,
therefore, improves the efficiency of the lamp,
so it gives more light for the same electricity
consumption. The incandescent filament of a
lamp is very bright and if you look directly at
it, especially at short range, the glare can hurt
your eyes.
That is why it is important to use properly
designed light fittings with diffusing material
which spreads the light, but shields the
filament from view.
Luminescent lighting
Electricity flows through metals and it will
also flow through gases and vapours under
some conditions. If special gases or vapours
are enclosed in a glass tube and the voltage
and gas pressure, together with other
factors, are correctly chosen, a current can
be passed through the tube which causes
the gas to become luminous.
This principle is used in neon signs, mercury
and sodium street lamps and fluorescent
tubes. Gases and vapours glow with
characteristic colours: for example, neon
gas gives red light; mercury vapour- bluish
green; and sodium vapour-yellow.
In the fluorescent lamp, for example,
mercury vapour is used. When current is
passed through this vapour, ultra-violet
energy is produced.
A fluorescent powder coating which has
been placed on the inside of the tube wall
absorbs the ultra-violet energy and, in turn,
glows and gives off visible light. Different
fluorescent powders give different colours
and with a suitable mixture, daylight or white
light, can be produced.
In either incandescent or luminescent
lamps, only a portion of the electrical
energy is turned into light energy. The
remainder is converted into heat energy
and is not available for the production of
light. Luminescent lamps change a greater
proportion of electrical energy into light
energy than incandescent lamps. That
means they consume less electricity for the
same amount of light produced. Luminescent
lamps are however more costly and the
fittings are more complicated.
The majority of street lights are controlled by
light sensing cells. These cells automatically
switch lights on as daylight fades in the
evening and off as daylight increases in the
morning. The cells are designed in such a
way that if one is defective; it causes the
lights it controls to remain switched on. This
avoids having areas left without lighting at
night.
Mechanical energy
If a current passes through a conductor
which lies in a magnetic field, there will
be relative motion between the conductor
and the field. This is the principle on which
the electric motor works. This is the reverse
of the <principle of generator operation>.
The electric motor takes in electrical energy
and gives out mechanical energy as rotary
motion. The motor is used to turn the
wheels of industry, drive trams, or operate
vacuum cleaners and refrigerators and
many other labour-saving devices in our
own homes. This is another example of how
energy may be changed from one form into
another.
Electricity has allowed people to enjoy a
higher standard of living with more goods
available and more time for recreation.