KEY CONCEPTS

To start I'm going to give the key concepts of this unit, the key concepts are a small sumary of the important part of the unit:

• Plastics consist 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(against electricity,heat and sound) ductile, malleable, impermeable adn light.
• There are three tyoes of plastic recycling processes:Chemical and mechanical recycling and energy recovery.
• Thermoplastics are usually made from petroleum products.The most common thermoplastics are:Polyethylene terephthlate(PET), high-density polyethylene, polyvinyl chloride(PVC),low-density polythylene, polypropylene, moulded polysthyrene and expanded polystyrene or Styrofoam.
• Thermosetting plastics are made from petroleum products.They include:Polyurethane, bakelite, melamine and polyester resins.
• Typical elastomers include rubber and neoprene.
• 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.
• Modification techniques use tools and machines to make changes to prefabricated materials, such as sheets,bars and mouldings.
  
• Example of these techniques include:measuring->drawing->marks and lines->cutting->drilling->filing and sanding->joining.
• You must always pay special attetion to health and safety rules.
• Both natural and synthetic fibres can be woven to make a variety of textiles.
• Natural fibres may come from animal sources(woll,silk), plant sources(cotton,linen,esparto,bamboo) and mineral sources(gold,silver and copper fibres).
• Synthetic fibres, such as nylon,polyester,rayon and Lycra, are plastic materials.

UNIT 5 PLASTICS AND TEXTILES

Today, we are going to start a new unit and in this unit you will learn to:

• Understand the properties and applications of plastis and how they are made.
• Classify plastic materials(thermoplastics, plastics and elastomers) and identify their basic applications.
• Identify different types of plastic in the most typical technical applications.
• Understand industrial processes and apply techniques correctly while following appropiate health and safety rules.
• Evaluate the environmental impact of the exploitation, transformation and disposal of plastic materials, as well as the benefits of recycling.
• Understand the properties, classification and production of textiles.
• Identify different textiles by their applications.

I hope which this unit you like.

8)ELECTRONS

TRANSISTOR
Transistor are basic components of electric circuits.They are made from semiconductor materials and have three electrons called the base,the collector and the emitter.
There are two types of transistor:NPN and PNP

Each electrode of a transistor is connected to a semiconductor material which either releases electrons(N) or accepts electrons(P).
To understand how transistors work, we can compare them to the water pipe system in the picture below. A small electric current in the base(B) controls the flow of water(electrons) between the collector(C) and the emitter(E).

• When no electrons are flowing through the base,then no electrons can pass from the collector to the emiter.The transistor is in cut off.
• 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.
• 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 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 picture illustrate the concept of transistor gain.

In the fist circuit,only a small current is flowing,so the bell does not ring.In the second circuit,the transistor multiplies the flow of electrons though the base by one hundred,As a result,the current that passes through the collector is one hundred times stronger.
BASIC DEVICES MADE WITH ELECTRONIC COMPONENTS
We can build various devices with the electronic components discussed in the previous section.Here are two types:
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.
-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 button, current flows through the base, the transistor is activated,and LED turns on.The capacitor also begins to charge itselfs.
-When we release the button, the LED continues to produce light for some time,using current from the capacitor.When the capacitos runs down, the transistor cuts off and LED turns off.
INTEGRATED CIRCUITS
Integrated circuits consist of miniature electronic components, such as transistors, resistors and capacitors.

8)ELECTRONICS

Electronics involves the study of circuits and components that modify the intensity, direction or properties of electric currents.
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 current.Its value, which we meausre in ohms, is indicated by a code of colours and numbers.

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

VARIABLE RESISTANCE OR POTENTIOMETER

The value of a variable resistance or potentiometer can be adjusted between zero and the maximum value specified by the manufacturer.

RESISTANCE THAT DEPENDS ON A PHYSICAL FACTOR

The physical factrs that effect resistance may be temperature or the amount of light,for example.

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

          -Negative temperature coefficient(NTC):The resistance decreases as the temperature rises.

          -Positive temperature coefficient(PTC):The resistance increases as the temperature rises.

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

CAPACITORS

Capacitors are components that can store an electrical charge.

The value of a capacitor indicates the charge in volts that it can store. This is measured in farads(F):

DIODES

A diode 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(A) and a cathode(K).

A LED(light emitting diode) only gives off light when an electric current flows through it.

For finish you can watch this video,surely it help you for understand: https://www.youtube.com/watch?v=JNi6WY7WKAI

7)ELECTROMAGNETIC CONTROL SYSTEM

The sistem which you can watch down is completely automatic.The cam on the side of the puley pushes the two metal contacts together for a short period of time.This happens once every time the pulley makes a complete circle, producing an intermittent light.

An electromagnetic control system activates the various parts of machine, at the right moment and for the right amount of time, ensuring that the machine functions properly.

CAM SWITCH CONTROLLER

The device on the side of pulley in the picture above is called 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 light bulb.

LIMIT SWITCHES
The picture below shows an electrical control system for a water tank.The battery provides power for the pump, which moves water from the lower tank to the upper tank.When the upper tank is full, a limit switch turns off the pump.

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

In this video you will learn:What is a limit switch

https://www.youtube.com/watch?v=P7y0TSsAlFw

6)ELECTROMAGNETIC MECHANISMS

Electromagnetic mechanisms are devices that convert movement into electricity or vice versa.In other words, they use electromagnetic phenomena to produce electricity or convert it into mechanical energy.

ELECTROMAGNETIC GENERATORS

Electromagnetic generators transform mechanical energy into electricity.There are two types of generators, depending on the type of current that is produced.Generators that produce direct current are called dynamos, and those that produce direct current are called dynamos, and those that produce alternating current are called alternators.

DYNAMOS

A dynamo consists of a magnet and a rotary coil.The coal is located between the two poles of the magnet.The ends of the coil have two semi-circular conductors, which form the commutator.These conductors are attached to carbon brushes, which in turn are connected to electrical wires.When electricity is applied to the coil, rotates and begins to generate direct current in the coil.

A simple dynamo with only one coil produces a pulsating direct current.If the dynamo has two or more coils at different angles, a more constant flow of direct current is produced.

In this video, we can watch the functioning of a dynamo: https://www.youtube.com/watch?v=RMM-TVtmRgQ

ALTERNATORS

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

ELECTRIC MOTORS

An electric motor is a device that can transform electrical energy into movement.It uses the forces of attraction and repulsion between a magnet and an electrically-charged wire.

In this video, we can watch the working of electrical motor: https://www.youtube.com/watch?v=DA6FdbpSefU

RELAYS

A relay 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 contact.When the electricity stops flowing, the moveable contact goes back to its original position.

Relays may have a single circuit with one moveable contact.They may also have two or four circuits, in which case they are called two-or four-pole relays.

5)EFFECTS OF ELECTRIC CURRENT

ELECTROMAGNETIC EFFECTS
The electric circuit has created a magnetic field.This effect can be used to produce movement,for example in electric motors, relays and other devices.
The scientist Michael Farady discovered the opposite effect.He noticed that electricity could be generated by using a magnet and an electrical conductor.This principle allows us to build dynamos and alternators.
To generate an electric current with a magnet, we can move the conductor or we can move the magnet.

SOUND

We can transform electric current into sound by using electromechanical devices, such as bells and buzzers. Some of these devices are based on the piezoeletric effect, or the ability of some materials to change shape when electricity is applied to them.

5)EFFECTS OF ELECTRIC CURRENT

The movement of electrons though conductive materials produces effects that have useful applications
HEAT
The movement of electrons through an electrical cabe is both slow and disorderly.The electrons often collide, increasing the temperature of the cable itself.
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
Most of energy that is consumed by radiators and heaters is converted into heat.

LIGHT
There are various ways that electricity can be used to produce light.We can use an electronic device called a light-emitting diode(LED)
INCANDESCENT BULBS
When an electric current passes through the metallic filament of a light bulb, it produces light. This phenomenon is called incandescence.

FLUORESCENT TUBES
Inside a fluorescet tube, there is a metallic filament, normally made of tungsteen.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.These react with mercury, creating invisible, ultraviolet light.Then the phosphor coating the tube transforms the ultraviolet light into visible light.
Unfortunately, fluorescent tubes contain a number of toxic substances, such as phosphor and mercury.

LIGHT-EMITTING DIODES(LED)
A light-emitting diode(LED) has layers of semiconductor materials.The n-type layer has extra electrons with negatively charged particles.In contrast, the p-type layer has holes where there aren't enough electrons.When electricity is applied to the LED,the electrons and holes cross over into the active layer, where they combine and produce photons, or particles of light.

4)TYPES OF CURRENT

DIRECT CURRENT
Between the terminals of a battery, there is a continuos,stable flow of energy. If we use a volmeter 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 connected a light bulb to a battery, the electrons always flow in the same direction with the same current.
ALTERNATING CURRENT
In alternating current the flow of electrons changes direction 50 times every second,as if the positive and negative poles of the socket were constantly changing places.In addition, the electric current is not always the same.
If we measured the voltage 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 become negative and decreases to -325V.
• The current increases to 0V.

The variation of any electrical parameter over a period of time is an electrical signal.
The tension or voltage of domestic electricity is an alternating signal because it alternates between positive and negative values.Its waveform is also sinusoidal, with a smooth, regular shape.
Alternating current is produced by generators, such as the ones in large electrical generating stations.There are stations may use conventional source of energy or non-conventional sources.

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 sinusoidal current, the average power would be as follows:
                                              Vef=Vmax/Raíz cuadrada de -2
TRANSFORMERS
There is an important difference between alternating and direct current.Alternating current can be increased or decreased by a transformer.This allows us to transfer electrical energy at very high voltages and over hundrers of kilometres,without losing any of the energy as heat.
Transformers consit of two windings made of copper wires.If we apply an alternating current to one of them(V1), it will be produce a certain voltage in other(V2).The value will depend on the number of times that the copper wire has been wrapped around each winding, represented as n1 and n2:
                                    V1/V2=n1/n2

3)TYPES OF CIRCUITS

SERIES CIRCUIT
Two or more elements form a series circuit when output of one element provides the input for the next element.
In the following diagram, the same current flows through all the elements, and the total voltage is the sum of the tensions at the end of each element.
.
To calculate the total resistance of a circuit, we add the resistance values of each load:R1+R2
PARALLEL CIRCUIT
In the parallel circuit, the various components share the same input and output.In other words, the wires from both sides are joined together.In this case, the potential difference is the same of each element, but the current that flows through each branch is different.The equivalent resistance of this type of circuit would be:
                                        1/R=1/R1+1/R2+1/R3
If identical batteries are connected in parallel,the voltage of the circuit will not increase. However, the total consumation of energy will be shared between the batteries, so each one will last longer.

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

In this type of circuit, the current remains constant between elements that are connected in series.At the same time, the voltage remains constant between elements are connected in parallel.

2)ELECTRICAL QUANTITIES

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ELECTRICAL RESISTANCE: OHM'S LAW
The resistance(R) of a material is equal to the voltage divided by the intensity of electric current which travels through the material. This ratio, which is called Ohm's Law, can be expressed as follows:
                                                         R=V/I
Ohm's law have other two forms:
                                           V=R*I          I=V/R
ELECTRICAL ENERGY AND POWER
Electrical energy
If a 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
The electric power of a load is the amount of energy that it can transform over a certain amount of time.Electric power is measured in watts(W) or kilowatts(kW).
If a electric current(I) flows at a particular tension(V), we can calculate the power(P) that is consumed:
                                                  P=V*I
The electrical energy that is consumed can be expressed as a function of power and time, using the kilowatt per hour(kW/h) as a unit of measurement.
If we know the power of a load, we can calculate the electrical energy that it consumes 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

VOLTAGES OR POTENTIAL DIFFERENCE

The amount of energy that a generator can be transfer to electrons depends on its voltage(V) or electric tension. This is measured in volts(V).
If we want to meausure the voltage, we can use volmeter. This divice has two wires that must be connected in paralell to the element that we are checking.

MEASURING ELECTRIC CURRENT
Electric current(I) is the change or number of electrons that flow through the cross-section of a conductor every second. We can express this mathematically as flollows:
                                 I=Q/t
Electric current is measured in amperes or amps(A) in the international system.
We can use an ammeter to measure electric current.