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.