Key concepts

• 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 plastics is called polymerisation.
• Plastic materials are resistant, insulating (aganist electricity, heat and sound), ductile, malleable, impermeable and light.
• Threre are three types of plastic recycling processes: chemical and mechanical recycling and energy recovery.
• Thermoplastics are usually made from petroleum products. The most common thermoplastics are: 

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

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

      - Polyurethane

      - Bakelite

      - Melamine

      - Polyester resins

• Typical elastomers incluide 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 or moulding.
• 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)
• Synthetic fibres, such as nylon, polyester, rayon and Lycra, are plastic materials.

Basic devices made with electronic components

Timers

A timer is a device that operates for a certain period of time and then shuts itself off automatically.

Integrated circuits

Integrated circuits consist of miniature electronic components, such as transistors, resistors and capacitors.

Transistors

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.

Diodes

A diode is an electronic component made from semiconductor materials. a diodes has two electrodes: an anode and a cathode.

A LED only gives off light when an electric current flows through it.

Capacitors

Capacitors are components that can store an electrical  charge.

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

Resistance that depends on a physical factor

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

- 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 decreases as the amount of light increases.

Variable le resistance or pontentiometer

The value of a variable resistance or pontetiometer can be adjusted between zero and the maximun value specified by the manufacter.

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 code of colours and number.