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.

Electronics

Electronics involves the study of circuits and components that the intensity, direction r properties of electric currents.

Limit switches

Limit switches are contact sensors that display an electrical signal, in the presence of a mechanical movement. They are widely used in industrial environments to censor the presence of objects in a specific position. They are used in various applications.

Cam switch controller

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

Electromagnetic control systems

An electromagnetic cotrol systems activates the various parts of a machine, at the right moment and for the right amount of time, ensuring that the machine funtions properly.

Relays

A relay in a electromagnetic component that works as a switch. The coil attracts a moveable metal contact towards another fixed contact. When the elctricity stops flowing, the moveable contact goes back to its original position.

Electric motors

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

Electromagnetic generators

Dynamos

A dynamo consists of a magnet and rotary coil. These conductors are attached to carbon bruses, which in turn are connected to electrical wires. When electricity is applied to the coil, it rotates and begins to generate direct current in te coil.

Alternators

A simple alternator nis almost to a dynamo, except for the commutator, which consists of two matallic rings connected to carbon bruses instead of direct current, this produces alternating current.

Electromagnetic mechanisms

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

Sound

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

Electromagnetic Effects

In this experiment, the elctric circuit has created a magnetic field. This effect can be used to produce movement.
The scientist Michael Faraday discovered the opposite effect. He notice that electricity could be generated by using a magnet and an electrical conductor. This priciple allows us to build dynamos and alternators.

Light

Incandescent bulbs

When an electric current passes throught the metallic filament of a light bulb, it produces light. This phenomenon is called incandescence.






Fluorencent tubes


Inside a fluorencent tube, there is a metallic filamen, normally made of tungdten. There is also an inert gas, such as argon, and a small amount of mercury.



Light- emitting diodes (LED)

A light-emitting diode (LED) has layers of semiconductor materials.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.

Heat

The energy that an electric current produces as heat is called the Joule Effect. It is expressed by the following formula:

E = I^2 x R x t

Most of the energy that is consumed by radiators and heaters is converted into heat.

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

The effinciency 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 follow.

Vef = Vmax / 1,41

Alternating current

The variation of any electrical parameter over a period of time is an electric 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.

Direct current

Between the terminals of a battery, there is a continuous, stable flow of energy

                                                       .

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.

Combation circuits may connect both power sources and loads in different ways:

Parallel circuit

If identical batteries are connected in parallel, the voltage of the circuit will not increase. However, the total consumption of energy will be shared between the batteries, so each one will last longer.

Series circuit

Two or more elements form a series circuit when the output of one element provides the input for the next element.

To calcule the total resistance of a circuit, we add the resitance valvues of each load:

                                                          R=R1+R2+R3+...

One example of this type of connection would be a series of generators. The totral resistance woulbe the sum of all the resistance values.

Electrical energy and power

Electrical energy

If an electric current flows at a  particular tension for a certain amount of time, we can calculate the energy that is consumed: E=V x I x t

In the SI, this electrical energy is measured in joules (J)

Electrical power

The elctric 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).

Electrical resistance: Ohm's Law

The resistance of a material is equal to the voltage divided by the intensity of the electric current which travels throught the material. This ratio, which is called Ohm's Law, can be expressed as follows:

                                                                  R=V/I

                                                           
Ohm's Law has two forms:

                                                       V= RxI       and         I=V/R

Measuring electric energy

Electric current is the charge or number of electrons that flow throught the coss section of a conductor every second. We can express this mathematically as foollow:
                                                                         
                                                                      I= Q/t

Elctric current is measured in amperes or amps in the international System or SI.

Voltage or potential energy

The amount of energy that a generator (electrochemical cell or battery) can transfer to electrons depends on its voltage or electric tension. This is measured in volts.

Diagrams and symbols

Electric circuit

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

Electric current is a continuous flow of electrons throught a circuit.

Parts of an electric circuit

Electric circuits consist of various parts:

Generators: provides the energy that electrons need in order to move.

Loads: are devices that transform electrical energy into other types of energy that we can use.

Switching devices: are used to direct and interrupt the flow of electric current.

Recycling

The recycling saves water and reduces the emission of greenhouse gases into the atmosphere.

The following table indicates the amount of energy thet is saved by recycling common, everyday materials

Energy efficiency

An energy-efficent device reqires less energy to perform the same work.

We can apply strategies of energy efficiency in many areas of daily life.

Lighting: We can reduce the amount of electric light that we use by talking advantage of natural lighting.
Domestic appliances: We can reduce consumption by unplugging devices that we are not using.
Air conditional and heating: We use a lot of energy to keep our homes at a comfortable temperature, but there are ways we can be more efficient.
Transport: The public transport we use when going long distances and the short distances we use the bycicle
.

Greenhouse effect

Climate change

Environmental impact assessment

Geothermal power stations

Geothermal power stations use natural heat from the deepest underground layers of out planet. This heat comes to the Earth's surface as hot water, stream and hot gases.

Geothermal energy can be used in two ways:

• It can be used directly to provide hot water for heatingand industrial uses. insome places, this hot water is used for bathing and health spas.
• It can be used indirectly to drive generators and produce electricity.

Marine power stations

Marine power stations use the movement of ocean water to generate electricity. There are three general types of marine power stations:

• Tidal power stations, which use the energy of tides 
• Wave power stations, which use the energy of waves.
• Ocean thermal conversion stations, which use the difference in water temperature between the surfece of the ocean and deeper areas to produce energy.