unit6.electricity

8/2/2019 Unit6.Electricity

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Unit 6. Electricity6.1Electricity6.2 Electric current6.3 Electric magnitudes

6.4 Ohms law6.5 Electric Circuit

Elements

Symbols6.6 Electric Associations6.7 Electric energy production

6.8 Electric Power


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6.1 The electricity

What would happen if we didnt haveelectricity?

?


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6.1 Electricity

1 Exercise: Write down a listof 20 objects that use

electricity
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6.1 Electricity

However we have to remember that we candecrease the amount of energy that wewaste everyday, helping our sustainable

development.


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6.1 Electricity

But, what is electricity ?The concept of electricity includes all

the phenomena related to theelectric charges
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6.1 Electricity

Matter is formed by atoms , which containinside smaller particles with electriccharges:

The electrons and protons

Atom

Electron

Proton
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6.1 ElectricityElectrons and protons have negative and

positive charges respectively

Protons

Electrons


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6.1 Electricity

These charges create forces betweenthem that can be attraction or repulsionforces according to the value of thecharge:

Equal charges: repulsionDifferent charges: attraction

attraction repulsion repulsion


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6.1 Electricity

Matter can be electrically charged whenthe charge distribution is upset

For example, we can change the chargedistribution of a pen by rubbing itagainst your hair. Then you can attractsome pieces of paper


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6.2 Electric currents

How can we move the charges?If we want to move the electric charges we

have to create a charge upset betweentwo elements and then connect them

Charge upset Charge equilibrium


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How can we move thecharges?

For example, a battery has apole with more negativecharges, so when we connectthem the charges startmoving in order to balancethemselves

We are creating anelectric current


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We can make all the charges movecontinuously through a matter, creating

an electric current.

The electric current is the displacement ofthe electrical charges (electrons)

through the matter

Electrons


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What is the electriccurrent used for?

Thanks to the chargesmovement we cantransform electricenergy into other

energies that are moreinteresting for us

Magneticenergy

Mechanicalenergy


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Calorificenergy

Light energy

Mechanicalenergy

Magneticenergy

Electric energy

The electric current canbe transformed into theseenergies.

Also, you can get theelectricity back from theseenergies, so, it isreversible energy.


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Exercise. Homework

2 ExerciseYou have to look for all

the electricmachines that youhave at home. Writedown their names

and which energythey use.Ten at least

Electricmachine

Energy

Cooker Calorofic energy


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6.3 Electric magnitudes

In order to understand electricity we have toknow first the main electric magnitudes:

VOLTAGEINTENSITYResistance


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6.3 Electric magnitude. Voltage

The electrons need energy to be able tomove through a material, this is theVoltage

We define the Voltage as the energy percharge unit that makes them flowthrough a material. This magnitude ismeasured in Volts.

Energy
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6.2 The electric current

To better understand the concept of theelectric current we can think of it as astream where the drops are the electric

chargesWe use the waterpower from the

drops movement tocreate energy, as theelectrons do.Stream
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We can see that the stream will havemore strength if there is more water inthe tank. Its similar to what happenedto the electricity

Lesswater pressure

Morewater pressure


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The higher the Voltage is the moreenergy the electric charges will have tokeep on moving

Lower voltage

Higher voltage


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6.3 Electric magnitude. Intensity

Intensity is the amount of charges thatgoes through a conductor per time unit.It is measured in Ampere

Lower intensity

Higher intensity


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6.3 Electric magnitude. Resistance

Electric resistance is the opposition tothe movement of the charges through aconductor. It is measured in Ohms

Lower Resistance

Higher Resistance


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Electric resistance is the opposition tothe movement of the charges through aconductor. It is measured in Ohms

Lower Resistance

Higher Resistance


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6.4 Ohms law

Ohms law links the threeelectric magnitudes as isshown:

R

V I = V= Voltage (volt V)I= Intensity (ampere A)

R= Resistance (ohm )


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6.4 Ohms law

Intensity is directly proportional to voltage :If the voltage is high the charges will have a

lot of energy, therefore the Intensity willbe high too

R

V I =
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6.4 Ohms law

Intensity is inversely proportional toResistance

If there is a high Resistance there will be alow intensity

R

V I =the charges will cross thematerial slowly


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6.4 Ohms lawCalculations with Ohms law

Exercise 3 :Justify how the Intensity will be if:

We have a low voltage VWe have a low Resistance R

RV I =

RV I =


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4 Exercise: Explain how the Intensitywill change if:We increase the Resistance and theVoltageWe decrease the Resistance and weincrease de VoltageWe decrease the Resistance and theVoltageWe decrease the Resistance and theVoltage


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In order to calculate thevalue of any electricmagnitude, we need to

know the value of theother two, and use Ohmsformula:

For example, if we want toknow the value of I andwe know that R=20 V=80V:

A I

I

R

V I

4

420

80

=

==

=

S l ti


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5 Exercise:Calculate the value of

the circuitmagnitudes in thesecases:

RV I =

V (V) R ( ) I (A)

2 2

2 4

2 4

10 5

5 10

20 1000

Solution


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6.5 Electric circuit

An electric circuit is a group ofelements that allows us to controlelectric current through a

material. We need:1.Generator2.Control element3.Receptors4.Conductor5.Protection

elements
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6.5 Electric circuit. Elements

The essential elements in a circuit are:1.- Generator : it creates an electric current

supplying voltage to the circuit. They can be:Batteries : they supply electric current but only for ashort time.Power supplies : they give a constant and continuouselectric current.
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6.5 Electric circuit. ElementsThe essential elements in a circuit are:2.- Control elements : we can manipulate

the electricity through the circuit.

Switch:

Push button:

Diverter switch
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the electricity through the circuit.Switch: It keeps the ON or OFF positions.

For example the switch lights at the bathroom

Push button:

Diverter switch:


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the electricity through the circuit.Switch:

Push button: The On position only works while you are pressing the button. For example thedoor bell

Diverter switch


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the electricity through the circuit.Switch:

Push button:

Diverter switch: it is used to switch a light onor off from different points in the same room,as you have in your bedroom


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6.5 Electric circuit. Elements3.- Receptors : they are the elements that

transform the electric energy into otherones that are more interesting for us.For example

Incandescent lights:

Engine:

Resistance:
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6.5 Electric circuit. Elements3.- Receptors :

For exampleIncandescent lights: when the electriccurrent goes through the lamp filament itgets really hot and starts emitting light.

Engine:

Resistance:


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For exampleIncandescent lights:

Engine: the electricity creates a magneticfield that moves the metal elements of

the engineResistance:


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For exampleIncandescent lights:

Engine:

Resistance: we use it to decrease theintensity of a circuit


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4 Conductor : all the elements haveto be connected to a material thattransmits the electric charges.


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4 Conductor :Conductors and devices have to be

insulated to protect us fromdischarges that can hurt us


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4 Conductor :

The circuit has to be CLOSED in orderto allow the electricity to circulatearound it from the positive to thenegative pole .


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6 Exercise :a)Name and draw 10 electric

receptors like a bulb lamp,engineb)Make a table with 10 insulating

and 10 conductive material


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6.5 Electric circuit. ElementsExercise 3

Which one of these lamps will give light?


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Exercise 4Will this lamp turn on?

Solution


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5.- Protection elements: they keepall the circuit elements safe fromhigh voltage rises, that can

destroy the receptorsFuse:

Circuit breaker:


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5.- Protection elements:

Fuse: the first one will blow, cutting

the circuit, in case of a voltage rise.They are easily replacedCircuit breaker:


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5.- Protection elements:

Fuse:Circuit breaker: they are used in newelectric installations, at home or in

factories. If there is a voltage rise, you dont have to replace them, onlyreload.


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6.5 Electric circuit. Symbols

Electric symbols are used to representelectric circuits with drawings that replacethe real circuit elements.


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6.5 Electric circuit. SymbolsGenerator

Battery

Battery association

Conductors :

When two conductors are crossedwithout any contact we indicate it with acurve


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6.5 Electric circuit. SymbolsControl elements

Push button

Switch

Diverter switch


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6.5 Electric circuit. SymbolsProtection elements

Fuse

Receptors :Lamp

Resistances: they have two symbols

Engines


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7 Exercise : Draw the following circuit usingelectric symbols


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6.6 Electric associations

The behaviour of electric elementsdepends on how they connect to eachother.

There are three possible configurations :1.Series2.Parallel3.Mixed


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6.6 Electric circuits

SERIES circuitThe series circuit connects the electricelements one behind the other

In this way, there is only one connectionpoint between elements

1 & 2 are connected only by A

2 & 3 are connected only by B


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PARALLEL associationIn this association, all the elements areconnected by two points

So, 1, 2 & 3 are connected by A and B


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MIXED associationA mixed association has elementsassociated in parallel and in series

1, 2 & 3 are in parallel and all of them arein series with 4


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10 ExerciseWhich of these elements are associatedwith series, parallel or mixed circuits?

Name the connection points withletters

Solution


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11 Exercise:Which of these elements are associatedwith series, parallel or mixed circuits.Name the connection points withletters

Solution


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6.6 Electric associations12 ExerciseWhich of these elements are associated with

series, parallel or mixed circuits. Name theconnection points with letters

Solution


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But what happens to receptors when theyare connected in series or parallelassociations?

Series and parallel associations changethe value of intensity and voltagethrough receptors

6 6 El t i i ti


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6.6 Electric associationsVoltage

Series ParallelVoltage is distributedbetween elements, that isthe reason why they have

less energy for eachlamp, so the light islower.

Voltage is the same in allelements, so all thelamps have the same

energy and the light ishigher.

Intensity


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IntensitySeries Parallel

All the lamps are in line,so they create a highresistance, that is thereason why the intensityis lower but the batterywill have a longer life.

All lamps are separated sothey create a lowresistance, that is thereason why the intensitythrough the lamps ishigher, but the battery willhave a shorter life

Circuit


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Circuit

Series Parallel

If there is any cut alongthe conductor, theelectric current will notbe able to go from the

positive to the negativepole.

If there is any cut alongthe conductor, theelectric current can gothrough any other way

CUT


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If there is any cut in series association

the water cant go further. But inparallel association there will be noproblem

cut


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6.7 Electric energy productionElectricity generation started when

Alessandro Volta made the firstelectric battery

Alessandro Volta(1745-1825)


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6.7 Electric energy productionHans Christian Oersted discovered that a

electric current can disturb a compass.

Alessandro Volta

(1777-1851)The same happens when we put close a

magnet, so he concluded that thecircuit created an artificial magnet .


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6.7 Electric energy production


Mr MichaelFaraday hadan idea, if aelectriccurrent cancreate anartificialmagnet

Can a magnetcreate anartificialelectriccurrent?


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6.7 Electric energy production


YES!!!!So Mr Michael Faraday discoveredthat we can create electricity with amagnet that is moving near a closecircuit


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6.7 Electric energy productionNowadays, industrial power

stations use the Faradaysdiscovery .


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6.7 Electric energy productionThey use others energies to mov

a turbine that moves a circuitinside the magnet of thegenerator

Generator turbine


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6.8 Electric power From the generator of the Power Station

the electricity is transmitted to our home


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6.8 Electric power

What is the differencebetween a 100 W and 7 Wbulb lamp ?


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6.8 Electric power

This is a energy savinglight because itconsumes less energy

(7 W) than aincandescent

bulb light (100W)

We know it because W is theelectric power unit


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6.8 Electric power W is the unit of the Electric Power and it

express the energy consumed per timeunit of an electric device

IVP = P= Power (Watts W)V= Voltage (volt V)I= Intensity (ampere A)


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6.8 Electric power At home all plugs have 230 Volts, so if we

know the Power of a bulb lamp of 100W wecan calculate the Intensity through thelamp.

V230V100WP

=

=

0,34AI230100I

V

PI

IVP

=

=

=

=


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6.8 Electric power

The electricitythat we consumeis measured in

kwh and we payaround 0,1 /Kwh:


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6.8 Electric power

A kwh is the result of multiplythe Power and the hours of use:

hPPkWh =


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6.8 Electric power

In order to know the price thatwe have to pay we have tomultiply the Power in kwh by its

price 0,1 /kwh

0,1hP1,0PPrice kWh ==


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6.8 Electric power Lets Calculate how much we have to pay

when we use a washing machine for 2h if itconsumes 1500W

h2Time

1,5kw1500WP=

==

3kwhP25,1P

PhP

kWh

kWh

kWh

=

=

=

0,3Price

kwh

0,1kwh3Price

0,1PPricekWh

=

=

=


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A closedB open

A openB closed

A closedB closed

Engine

lamp 1

lamp 2

Point out in the table if the engine andlamps works for the following situations

Calculate the value of the intensity in


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Calculate the value of the intensity inthese cases:

V (V) R ( ) I (A)

8 2

7 2

4 8

300 6

21 7

1000000 20

6 4 Ohms law


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V (V) R ( ) I (A)

2 2

2 4

6.4 Ohm s lawCalculations with Ohms law 5 Exercise Solution

1AI

2

2I

R

VI ===

A5,0I 4

2I

R

VI ===

6 4 Ohms law


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V (V) R ( ) I (A)

2 4

10 5

6.4 Ohm s lawCalculations with Ohms law Solution

8VV24V

IR V

=

=

=

=

=

=

2R

5

10R

I

VR

6 4 Ohms lawexercise


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V (V) R ( ) I (A)

5 10

20 1000

6.4 Ohm s lawCalculations with Ohms law Solution

A0,5I 10

5

I

R

VI

=

=

=

20kvV

V00002V

200001V

IR V

=

=

=

=

6.5 Electric circuit. Elements Exercise


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The electric current always goes throughthe route with less resistance, like water

Here we have theresistance needed tocreate light

No resistance

6.6 Electric associations Exercise


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10 Exercise solutionred-series Blue: parallel

SERIES :1 and 2 are joined by A.

2 & 3 are joined by B3 & 4 are joined by C

MIXED:Series:1 is joined to 2 and 3 by AParallel: 2 and 3 are joined by A and

BSeries: 2 and 3 are joined to 4 by C

Exercise

6 6 El i i i


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6.6 Electric associations11 Exercise solution

Parallel : 1, 2 and 3are joined together by A and B

Series : 1 and 2 are joined by A; 2 and 3

are joined by B

Exercise

6 6 El i i iExercise


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6.6 Electric associations12 Exercise solution

Mixed:Series: 1 and 2 are joined to ASeries: 2 and the 4 & 3 association are joined by BParallel: 4 and 3 are joined by B and C

unit6.electricity

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