ELECTRICITY

INTRODUCTION 2

EFFECTS OF ELECTRICITY 3

ELECTRIC CIRCUITS 4
Symbols of electrical components 6

ELECTRICAL MAGNITUDES 7
Tension or Voltage (V) 7
Current (I) 7
Resistance (R) 7

OHM’S LAW 8

TYPES OF CIRCUITS 8
Series circuit 8
Parallel circuit 9
Mixed circuit 12
Association of batteries 12

MEASUREMENT OF ELECTRICAL MAGNITUDES 13

Current intensity – ammeter 13
Voltage – voltmeter 14
Resistance – ohmmeter 15

ELECTRICAL SAFETY 16

ELECTRICITY AND ENVIRONMENT 17

1.INTRODUCTION
Electricity completely surrounds us. For most of us, modern life would be impossible
without it. Here are just a few examples:
● Throughout your house, you probably find electrical outlets where
you can plug in all sorts of electrical appliances.
● Most portable devices contain batteries, which produce varying
amounts of electricity depending on their size.
● During a thunderstorm, there are huge bolts of electricity called
lightning that shoot down from the sky.
● It is easy to create electricity from sunlight using a solar cell; or you
can create electricity from the chemical energy in hydrogen and
oxygen using a fuel cell.

It is hard to imagine modern people living without electricity.

Matter is made up of atoms. Atoms contain particles called: protons, electrons and
neutrons.

● Protons have a positive charge

● Electrons have a negative charge
● Neutrons have no charge

Electrons are a fundamental part of electricity. In many materials, electrons can move
from one atom to another. This movement of electrons is the origin of electricity, in fact
the movement of electrons is an electric current.
If the electrons don’t move, the material doesn’t conduct electricity and is called an
insulator. Some materials which are electrical insulators are for example: wood, plastic,
glass, ceramic…
If the electrons can move through the material, it is an electrical conductor. For
example water and metals such as gold, silver, copper, iron:
● Copper is used for connecting wires.
● Nichrome has more resistance and is used in the heating elements of electric
fires.
Electrical circuits can be complex. But at the simplest level, you always have the source
of electricity (a battery, etc.), a device that uses it (a light bulb, motor, etc.), and two
wires to carry electricity between the battery and the load.
However, electricity can be very dangerous, too. Accidental contact with electrical
currents can cause injury, fire, extensive damage and even death. It is important to
remember that working with and around electricity requires your full attention and
respect.

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Most electricity comes from power stations that burn "fossil fuels" such as coal. The
heat boils water into steam, and the steam drives big turbines that generate electricity.
But there are big problems with this way of generating electricity. Burning fossil fuels is
very bad for the environment, as it creates pollution and also affects the climate of the
Earth. Fossil fuels are also running out. We all need to cut down on the amount of
electricity we use at the moment.

2.EFFECTS OF ELECTRICITY
Electricity is a strong invisible force that gives power to machinery, lights, heaters and
many other forms of equipment.
Moving electrons have energy. As the electrons move from one point to another, this
energy can provide:
● Heat: when the electrical current flows through a material, it heats.
▪ Toasters, hair dryers and space heaters turn electricity into
heat.
● Light: an electric current flowing through a material increases its
temperature and produces light.
▪ In an incandescent bulb, for example, the energy of the
electrons is used to create heat, and the heat in turn creates
light.
▪ Fluorescent lamps, LEDs … turn electricity into light.
● Movement:
▪ Electric motors turn electricity into motion.
● Sound:
▪ Speakers turn electricity into sound waves.
● Information:
▪ Computers turn electricity into information.
▪ Telephones turn electricity into communication.
▪ TVs turn electricity into moving pictures.
▪ Radios turn electricity into electromagnetic waves that can
travel millions of miles.

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3.ELECTRIC CIRCUITS
An electric circuit is an unbroken path along which
an electric current exists or is able to flow.
Components of an electric circuit

The basic components of a circuit are:

● Conductors
These are the wires that connect the
different elements of the circuit
which allow the flow of electricity.
The wires are usually made of
copper and covered with plastic in
order to isolate them.

● Power supply
This is a device that causes energy to flow through the circuit. A battery, a
generator or an alternator are examples of power supplies. All of them transform
a type of energy into electrical energy.
Batteries are used in small devices. They transform chemical energy into electrical
energy. There are different kinds, for example:

▪ Normal batteries, which are the

most commonly used.
▪ Alkaline batteries, which last
longer.
▪ Rechargeable batteries, which
can be recharged several times.
▪ Button batteries, which are
smaller but pollute the most.

All batteries contain toxic materials so they can not be thrown into the rubbish. There
are special containers for collecting and recycling used batteries.
Generators or alternators, which produces electrical energy in electrical power
stations.
● Output devices: Appliances
These elements receive electrical energy and
transform it into other types of useful energy
(light, heat, movement, sound, etc.). A bulb, a
heater, a motor or a bell are some examples of
appliances.

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 ▪ Bulbs: they transform electrical
energy into light.
▪ Motors: they transform electrical
energy into movement.
▪ Bells: they transform electrical
energy into sound.
▪ Heaters: they transform electrical
energy into heat.

● Control elements
These elements are used to control
circuits. You can use them to open,
close and switch between different
circuits. There are different kinds such
us push button switch, on-off switch,
2-way switch, etc.

● Circuit protection elements

If too much electrical current passes through

a wire, it heats up and a fire can start.
To avoid this, most electrical circuits,
including those in houses, use fuses (as
it’s shown in the figure on the left). A
fuse is a device -normally a wire- that
burns up and breaks if too much
electricity goes through it. The element
in the fuse melts, opening the circuit
and preventing other components of the
circuit from being damaged by the over
current.

To establish an electric circuit there must be two requirements:

1. A closed path for the electrons to flow.
2. An energy supply which creates an electric potential difference across the two
ends of the electrical circuit.

With only these two requirements we get a short circuit. The charge flows between
the terminals and a lot of energy is consumed. The circuit heats the wire to a high
temperature and a fire might break out.

In practice, electrical circuits are designed to serve a useful function. So the circuit
must have a bulb, a motor, a bell or a similar device that uses electricity for a specific
function.

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 3.1. Symbols of electrical components

Schemes are used to represent electrical circuits in which each element is identified by a
symbol.

Here you can see an example of an electrical circuit, containing some of these elements:

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4.ELECTRICAL MAGNITUDES

4.1. Tension or Voltage (V)

Voltage is the force that causes a current to flow. It is a measurement of the level of the
electrical energy. Voltage is measured in volts (V).

For example:
● A small battery used in an alarm clock has 1.5 volts.
● A button battery, as in a watch, can have 3 volts.
● Electricity at home is supplied at 230 volts.

For a flow of current there must be a different energy level between two points of the
circuit (voltage). A generator is the device that produces the voltage needed in a
particular circuit.

4.2. Current (I)

Current is the number of electrons flowing through a circuit in a second. It’s measured
in amperes (A).

4.3. Resistance (R)

Resistance is anything which opposes the flow of current in a circuit. The resistance is
measured in ohms (Ω)

For example:
● Longer wires have higher resistance.
● Resistance increases as the cross-sectional area of the wire decreases.
● Electrical insulators offer a very high resistance.
● Electrical conductors offer very low resistance.
● As temperature increases the resistance of a wire increases (this is used in a
resistance thermometer).
● Resistors can be used to control the current in a circuit.
● A variable resistor is used to adjust the flow of current in a circuit.

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5.OHM’S LAW
The relationship between current, voltage and resistance was discovered by George
Ohm. From experiments, he found that:

This expression can also be written in other ways:

Looking at the last equation we can see that if the voltage increases, but the resistance is
constant, the current also increases.

6.TYPES OF CIRCUITS
Circuits exist in all kinds of different places. The lighting in school or home, street
lights, torches and alarm systems all have circuits that are fairly simple.
Circuits are found in calculators, computers, televisions, radios, cars, medical
equipment, aircraft, the Internet, factories, telephones and many more places.
We shall look at some of these connections.

6.1. Series circuit

Components that are placed one after another in the circuit are connected in series. The
current that flows across each component has the same value.

The diagram on the right shows a circuit with two

lamps connected in series. If one lamp breaks,
the other lamp will not light.

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This circuit is another example of a series circuit.
Different types of components can be connected in
series.

6.2. Parallel circuit

If we connect several electric components
as shown in the figure on the right, we say
that they are connected in parallel.

The scheme on the right shows a circuit

with two lamps connected in parallel. If
one lamp breaks, the other lamp will
still light.

Series circuit Parallel circuit

Scheme of
the circuit

The effect is to reduce the resistance of the

The effect is to add more
circuit
resistance to the circuit
Resistance

The voltage of the supply

The voltage across each component in
is shared between the
parallel, is the same
Voltage components in series

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 The current that flows
across each component The current is shared between each
connected in series is the component connected in parallel
Current same

Examples of circuits:

Series circuit

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 Parallel circuit

V1=V2=V3 = 12 V

Series Circuit Parallel Circuit

Total resistance is smaller than the
Resistance Total resistance is greater than every
smallest of the resistance connected in
rules single resistance of the circuit
parallel.

Current is the same in every point of The sum of currents approaching a

the circuit junction is the same than the one
Current
As the number of appliances increases leaving that junction
rules
in the circuit, the resistance gets larger More current goes through the easier
and the current gets smaller path (the one with less resistance)
Total voltage is shared between all the
Appliances in parallel get the same
appliances of the circuit.
Voltage voltage
Battery voltage is equal to the sum of
rules Battery voltage is equal to the voltage
voltages in every appliance of the
in every appliance of the circuit.
circuit

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 6.3. Mixed circuit
If a circuit has components connected both in series and in parallel, we call it a mixed
circuit.

6.4. Association of batteries

Cells and batteries are useful sources of electricity. They transfer chemical energy to
electrical energy.
A zinc-carbon cell (dry Leclaché cell): This is the common cell used in torches. The
voltage across the cell is 1.5V. Once the chemicals are used up you throw it away.
There are also rechargeable batteries. For example, a lead-acid battery in a car turns the
starter motor and is then re-charged when the engine is running. During recharging,
energy is stored in the battery.
We shall look at some ways of connecting batteries.
● Batteries in series
When we connect in a circuit
several batteries in series, the total
voltage increases and the current
gets larger.
In circuit C, the batteries give 3
volts. The lamp will be very
bright.
As we can see, in circuit C, the
batteries give 3 volts. The lamp
will be very bright

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7.MEASUREMENT OF ELECTRICAL
MAGNITUDES

7.1. Current intensity – ammeter

An ammeter is an instrument which is used to measure the flow of an electric current in

a circuit.

Diagrams A and B below show a circuit before and after connecting an ammeter.
A B

● The ammeter must be connected in series with the resistor.

● Ammeters must have a LOW resistance.

(All the current flowing in the circuit must pass through the ammeter. As meters are not
supposed to alter the behaviour of the circuit, or at least not significantly, the ammeter
must have a very LOW resistance).

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 7.2. Voltage – voltmeter

A voltmeter is an instrument used for measuring the voltage between two points in an
electric circuit.

Diagram C shows the same circuit after connecting a voltmeter:

A C

● To measure the voltage, the circuit is not changed: the voltmeter is connected in
parallel.
● Voltmeters must have a HIGH resistance.

(This time, you do not need to break the circuit. The voltmeter is connected in parallel,
so it should take as little current from the circuit as possible. In other words, a voltmeter
should have a very HIGH resistance).

Voltage measurements are used much more often than current measurements.

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 7.3. Resistance – ohmmeter

An ohmmeter is an instrument used to measure the resistance of a particular component

of an electric circuit.

A D

To measure resistance, the component must be removed from the circuit.

If you want to measure the resistance of a particular component, you must take it out of
the circuit and test it separately, as shown in diagram D.

A multimeter or a multitester is an electronic measuring instrument that combines

several functions in one unit. The most basic instruments include an ammeter,
voltmeter, and ohmmeter.

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8. ELECTRICAL SAFETY
Electricity can light lamps, can work televisions and many other things we use in our
everyday life but it is important not to get in electricity's way because it can harm you.
Electricity can be dangerous, we need to take care and keep ourselves safe. If you
contact the electricity in an appliance, power cord, or power line, you could be seriously
injured or killed.

Here are some safety rules to help us:

● Respect the power of electricity.

● Never put anything into sockets.
● If you use and adaptor be careful not to overload the socket.
● Never poke anything into electrical machines.
● Never play with electrical cords, wires, switches, or plugs.
● If a plug or switch becomes hot in use turn it off.
● If an appliance works improperly or gives the slightest warning of a problem,
such as shocks or sparks, disconnect it and have it serviced.
● Never repair a break in an outdoor extension cord. Throw the cord away and buy
a new one.
● Protect cords from heat, chemicals and oil. Coil cords loosely when storing
tools. If cords are broken, get new ones or shorten them.
● Keep cords out of walking areas where people could trip over them.
● Don’t use appliances with a frayed flex or a cracked plug. Tell an adult about it
● Never use a hairdryer or play an electrical radio or television into the bathroom
or use them near any water.
● Make sure your hands are dry before you touch anything electrical.
● Never throw water on an electrical fire.
● Stay away from power equipment.
● Stay away from broken power lines. Tell an adult.
● Take extra precautions when using power tools. Your electrical wiring should be
adequate for the job. Circuits should be grounded. The tools should be insulated.
● If you encounter an electrical-injured victim, do not touch the person until they
have been freed from the source of electricity. You can use a non-conductor,
such dry rope or wood to push or pull the victim away from the power source.
● Stay away from substations and transformers.
● Inform your teacher of faulty equipment in the workshop

ELECTRICITY KILLS
MAKE SURE IT'S SAFE

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9.ELECTRICITY AND
ENVIRONMENT
The generation and use of electricity affects the environment. Engineers and scientists are
developing new environmentally-friendly ways of generating electricity. There are lots of
ideas such as: nuclear power, wind power, solar power, wave power, tidal power, and
biomass energy.

Below we can see some examples of the environmental impact of the electricity, both of
its generation and its use:

● The variety of fuels - coal, oil or natural gas - used to generate electricity has
some impact on the environment. The fossil fuels are burned to create steam.
This steam is used to turn a turbine which will move the electric generator. The
smoke and gas from burning fossil fuels pollutes the air. For example: sulphur
dioxide and NOx emissions contribute to acid rain and carbon emissions
contribute to global climate change.

● The force of water -used in a hydroelectric facility- to turn the turbines and the
generator disrupts the natural flow of a river with negative effects on fish and
water plants.

● Nuclear power plants are generating and accumulating radioactive waste.

● Some of the renewable energy facilities can affect wildlife (fish and birds) and
the disruption of land uses

Since electricity is very important in our daily lives, we are demanding more electricity
service everyday and we are polluting and increasing the damage to our environment.
We must avoid it by using electricity efficiently and obtaining it from the cleanest
sources available.

There are also, some things we can do to save energy in order not only to preserve the
world but either to save money, such us:

● Insulate your walls, windows and ceilings.

● Set your clothes washer to the warm or cold water setting, not hot.
● Make sure your dishwasher and wash machine is full when you run it
and use the energy saving setting, if available.
● Select the most energy-efficient models when you replace your old
appliances.
● Be careful not to overheat or overcool rooms.
● Buy energy-efficient compact fluorescent bulbs for your most-used
lights.
● Whenever possible, walk, bike, carpool, or use mass transit.
● Reduce the amount of waste you produce by buying minimally packaged
goods, choosing reusable products over disposable ones, and recycling.

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