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