5.TEXTILES:

KEY CONCEPTS:

• Both natural and synthetic fibres can be woven to make a variety of textiles.
• Natural fibres may come from animal sources(wool,silk),plant sources(cotton,linen,esparto,bamboo) and mineral sources(gold,silver and copper fibres).
• Sythetic fibres,such as nylon,polyester,rayon and Lycra,are plastic materials.

4.MODIFICATION TECHNIQUES:

KEY CONCEPTS:

• Modification techniques use tolos and machines to make changes to prefabricated materials,such as sheets,bars or mouldings.
• Examples of these techniques include:measuring -> drawing marks and lines -> cutting -> drilling -> filing and sanding -> joining.
• You must always pay special attention to health and safety rules.

3.PLASTIC FORMING TECHNIQUES:

KEY CONCEPTS:

• Various industrial techniques can be used to manufacture plastic products,such as:extrusion,calendering,vacuum forming and moulding.
• The main techniques for using moulds are as follows:blow moulding,injection moulding and compression moulding.

2.THE CLASSIFICATION OF PLASTICS.

KEY CONCETS:

1. Thermoplastics are usually made from petroleum products.The most common thermoplastics are:

• Polyethylene terephthalate(PET).
• High-density polyethylene.
• Polyvinyl chloride(PVC).
• Low-density polythylene.
• Polypropylene.
• Moulded polystyrene.
• Expanded polystyrene or Styrofoam.

 2. Thermosetting plastics are made from petroleum products.They include:

• Polyurethane
• Bakelite
• Melamine
• Polyester resins

 3. Typical elastomers include rubber and neoprene.

UNIT 3:PLASTICS AND TEXTILES.

1.PLACTIC MATERIALS:

KEY CONCEPTS:

• Plastics consists of long chains of atoms which are mostly composed of carbon.
• Plastics can be classified into natural and synthetic plastics.
• The process of manufacturing plastic is called polymerisation.
• Plastic materials are resistant,insulating(aganist electricity,heat and sound),ductile,malleble,impermeable and light.
• There are three types of plastic recycling precesses:chemical and mechanical recycling and energy recovery.

TRANSISTORS: Are basic components of electrical circuits.They are made from semiconductor materials and have three electrodes called the base,the collector and the emitter.
There are two transistor: NPN and PNP.

1. When no electrons are flowing through the base,then no electrons can pass from the collector to the emitter.The transistor is in cut off.
2. When many electrons are flowing through the base,the route between the collector and the emitter will be completely open.The transistor is in saturation.
3. When the flow of electrons through the base is between the cut off and saturation levels,it will be proportional to the flow of electrons between the collector and the emitter.The transistor is in the active region.

Transistor are the basic components of the microprocessors and memory circuits that are used in computers.The following pictures illustre the concept of transistor gain.











8.2.BASIC DEVICES MADE WITH ELECTRONIC COMPONENTS:
We can build various devices with the electronic components discussed in the previous section.Here are two examples:

TIMERS: A timer is a device that operates for a certain period of time and then shuts itself off automatically. We can use the circuit on the right as an example:

1. At first,the LED is off,since there is no current flowing through the base.The transistor is in cut off.When we push the botton,current flows through the base,the transistor is activated,and the LED turn on.The capacitor also begins to charge itself.
2. When we released the botton,the LED continues to produce light for some time,using current from the capacitor.When the capacitor runs down,the transistor cuts off and the LED turns off.

INTEGRATED CIRCUITS: Integrated circuits consist of miniature electronic components,such as transistor,resistors and capacitors.For example,the following UL-N2803A integrated circuit contains eight pairs of Darlington transistors.

CAPACITORS: Are components that can store an electrical charge.
The value of a capacitors indicates the charge in volts that it can store.This is measured in farads.











DIODES:  Is an electronic component made from semiconductor materials.It only allows electric current to flow in one direction.A diode has two electrodes: an anode and a cathode.
A LED only gives off light when an electric current flows throungh it.

8.ELECTRONICS:
Electronics involves the study of circuits and compenents that modify the intensity, direction or properties of electric currents.

8.1.ELECTRONIC COMPONENTS:
In this section,we will analyse the most common electronic components.

FIXED RESISTANCE OR RESISTOR: A fixed resistance or resistor opposes the flow of electric currents.Its value,which we measure in ohms,is indicated by a code of colours and numbers.








The first two stripes are replaced by two numbers,according to their color.The third stripe indicates the number of zeroes that we must add to the previous figure.The fourth stripe indicates the tolerance or the tolerance or the máximum deviation from the theoretical value.











VARIABLE RESISTANCE OR POTENTIOMETER: The value of a variable resistance or potentiometer can be adjusted between zero and the máximum value specified by the manufacturer.








RESISTANCE THAT DEPENDS ON A PHYSICAL FACTOR:

• Resistance that depends on temperature is called a thermistor.There are two types of thermisors:

1. Negative temperature coefficient:The resistance decreases as the temperature rises.
2. Positive temperature coefficient:The resistance increases as the temperature rises.

• LDR:Resistance that varies according to the amount of light received.The resistance decreases as the amount of light increases.These devices,like potentiometers,are often used in security systems,where they are parts of sensors.

7.ELECTROMAGNETIC CONTROL SYSTEMS:
An electromagnetic control system activites the various parts of a machine,at the right momento and for the right amount of time,ensuring that the machine funtions properly.

7.1.CAM SWITCH CONTROLLER:
The device on the side of the pulley in the picture above is called a cam.The shape of this device allows us to control the moment and duration of an activity,such as the running of a motor or the illumination of a light bulb.

7.2.LIMIT SWITCHES:
The switches is activated when the float rises to a certain level.When the wáter level goes down,the switch returns to its original position and the pump turns on again.There are two types of limit switch:

• Normally closed.
• Normally open.

6.2.ELECTRIC MOTORS:
An electric motors is a divice that can transform electrical energy into movement.It uses the forces of attraction and repulsion between a magnet and an electrically-charged wire.
















6.3.RELAYS:
Is an electromagnetic component that Works as a switch.When electricity passes through the coil,it acts like a magnet.The coil attracts a moveable metal contact towards another fixed contract.When the electricity stops flowing,the moveable contact goes back to its original position.

6.ELECTROMAGNETIC MECHANISMS:
Electromagnetic mechanisms are devides that can convert movement into electricity or vice versa.In other words,they use electromagnetic phenomena to produce electricity or convert it into mechanical energy.

6.1.ELECTROMAGNETIC GENERATORS:
Electromagnetic generators transform mechanical energy into electricity.There are two types:Dynamos and alternators.

DYNAMOS:Consists of a magnet and rotary coil.The coil is located between the two poles of the magnet. The ends of the coil have two semi-circular conductors,which form the commulator.These conductors are attached to carbón brushes, which in turn are conneted to electrical wires.When electricity is applied to the coil,it rotates and begins to generate direct current in the coil.









ALTERNATORS:A simple alternator is almost identical to a dynamo,except for the commutator,which consists of two metallic rings connected to carbón brushes.Instead of direct current,this produces alternating current.

5.EFFECTS OF ELECTRIC CURRENT:

5.1.HEAT:
The energy that an electric current produces as heat is called the joule effect.It is expressed by the following formula:
E= I2*R*t.


5.2.LIGHT:
There are various ways that electricy can be used to produce light.

Incandescent bulbs:When an electric current passes through the metallic filament of a light bulb,it produces light.The phenomenon is called incandescence.

Fluorescent tubes:Inside a fluorescent tube,there is a metallic filament,normally made of tungsten.There is also an inert gas,such as argon,and a small amount of mercury. When an electric current passes through the filament,electrons are emitted into the inert gas.

Light-emitting diodes:A light-emitting diode has layers of semiconductor materials.












5.3.ELECTROMAGNETIC EFFECTS:
In this experiment,the electric circuit has created a magnetic field.This effect can be used to produce movement.
The scientist Michael Faraday discovered to opposite effect.He noticed that electricity could be generated by using a manget and an electrical conductor.This principle allows us to build dynamos and alternators.













5.4.SOUND:
We can transform electric current into sound by using electromechanical devides,such as bells and buzzers.Some of these devides are based on the piezoelectric effect,or the ability of some materials to change when electricy is applied to them.

4.3.THE EFFICIENCY OF ALTERNATING CURRENT:
The average power of alternating current is equal to the direct current that is needed to produce the same effect.In the case of an alternating sinosoidal current,the average power would be as follows:
Vef= Vmax/√2
















4.4.TRANSFORMERS:
Transformers consist of two windings made of cooper wire.If we apply an alternating current to one of them(V1), it will produce a certain voltage in the other (V2) the value will depend on the number of times that the cooper wire has been wrapped around each winding,represented as N1 and N2:

V1/V2=N1/N2.

4.TYPES OF CURRENT

4.1.DIRECT CURRENT:
Between the terminals of a battery,theree is a continuous,stable flow of energy.If we use a voltemeter to measure the current in a car battery,the result will always be 12 volts.This is called direct current.In the same way,if we connect a light bulb to a battery,the electrons always flow in the same direction with the same current.

4.2.ALTERNATING CURRENT:
If we measured the voltaje of an electrical socket,the results could be represented in a graph like the one below:

• The current begins at 0V and increases to 325V.
• The current decreases from 325V to 0V.
• The current becomes negative and decreases to -325V.
• The current increases to 0V.

The variation of any electrical parameter over a period of time is an electric signal.
The tensión or voltage of domestic electricity is an alternating signal becouse it alternates between positive and negative values.Its waveform is also sinusoidal,with a smooth,regular shape.

3.TYPES OF CIRCUITS

3.1.SERIES CIRCUIT:
Two or more elements from a series circuit when the output of one element provides the input for the next element.
To calculate the total resistance of a circuit,we add the resistance values of each load:
R=R1+R2+R3+....

3.2.PARALLEL CIRCUIT:
If identical batteries are connected in parallel,the voltaje of a circuit will not increase.However,the total compsumition of energy will be shared between the batteries,so each one will last longer.

3.3.COMBINATION CIRCUIT:
A combination circuit has some elements connected in series and other elements connected in parallel.

• Three loads in a combination circuit.

• Four loads in a combination circuit.

2.3.ELECTRICAL RESISTANCE: Ohm's LAW:
The resistance (R) of a material is equal to the voltaje divided by the intensity of the electric current which travels through the material.This ratio,which is called Ohm's law,can be expresed as follows: R=V/I.












2.4.ELECTRICAL ENERGY AND POWER:










ELECTRICAL ENERGY: If an electric current (I) flows at a particular tension (V) for a certain amount of time (t) ,we can calculate the energy (E) that is consumed: E=V*I*t
In the SI,this electrical energy is measured in joules.(J).

ELECTRIC POWER:  If an electric current (I) flows at a particular tension (V),we can calculate the power (P) that is consumed: P=V*I.

If we know the power of a load,we can calculate the electrical energy that it cosumes over a certain amount of time.We simply multiply the power in kilowatts by the amount of time in hours.E=P*T
 

2.ELECTRICAL QUANTITIES

2.1.VOLTAGE OR POTENTIAL DIFFERENCE:
The amount of energy that of generator (electrochemical cell or battery) can transfer to electrons depends on its voltaje (V) or electric tension.This is measured in volts (V).
















2.2.MEASURING ELECTRIC CURRENT:
Electric current (I) is the charge or number of electrons that flow throungh the cross-section of a conductor every second. We can express this methemetically as follows: I = Q/t

Electric current is measured in amperes or amps (A) in the international system or SI.

1.2. DIAGRAMS AND SYMBOLS:

 

TEMA 7

1.AN A ELECTRIC CIRCUIT:

An electric circuit is a pathway for the flow of electrons.

1.1.PARTS OF AN ELECTRIC CIRCUIT:
Electric circuit consist of various parts:

• Generators provide the energy that electrons need in order to move.

cells and batteries:Electric current is generated by chemical processes.

• Loads are devides that transform electrical energy into other types of energy that we can use.

light bulbs:They produce light.

















motors:They produce movement.










resistors:They produce heat.










BELLS:They produce sound.

• SWITCHING DEVIDES are used to direct and interrupt the flow of electric current.

Switches,push butttons,3 way switches.

7.2.EFFECTS ON THE ENVIRONMENT:
Energy production includes many steps,from the extraction of natural resources to the transportation and final distribution of energy to consumers.Each of these steps can have an impact on the environement.

• Extracting natural resources
• Transporting fuel
• Generating fuel
• Waste treatment.

7.3.CLIMATE CHANGE:

• When we burn fossil fuels,gases such as carbón dioxide and methane are released into the air.These gases contribute to the greenhouse effect,which increases the earth's average temperature.
• Alredy we can observe some of the effects of global warmig,such as the melting of our polar ice caps and glaciers which lead to rising sea levels,and more extreme weather conditions in many places around the world.
• Power stations that burn fossil fuels also reléase other pullution into the air,such as sulphur oxide and nitrous oxide.These pollutants combine with wáter vapour in the air to produce acid rain,which damages our forest,lakes and rivers.It also contributes to the acidification of our oceans.
• These power stations effect plant and animal life because they use refrigeration systems that pump hot wáter into our rivers and oceans.This increases the local wáter temperature and also reduces the amount of oxygen in the wáter.
  

7.4.ENERGY CONSUMPTION:
The fossil fuels that consumers use in their cars or home heating systems also have an effect on the evironment.