KEY CONCEPTS OF TEXTILES

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, siver, and cooper wires).

Stnthetic fibres, such as nylon, polyester, rayon and Licra, are plastic materials.

KEY CONCEPTS OF MODIFICATION TECHNIQUES

MODIFICATION TECHNIQUES use tools and machines to make changes to prefabricated materials, such as sheets, bars or mouldings.

Examples of these techniques include: MEASURING  ⇒ DRAWING MARKS AND LINES ⇒ CUTTING ⇒ DRILLING ⇒ FILING AND SANDING ⇒ JOINING

KEY CONCEPTS OF PLASTIC FORMING TECHNIQUES

Various industrial techniques can be used to manufacture plastic products, such as: EXTURSION, CALENDERING, VACUUM FORMING and MOULDING.

The main techniques for using moulds are as follows: BLOW MOULDING, INJECTION MOULDING and COMPRESSION MOULDING.

KEY CONCEPTS OF THE CLASSIFICATION OF PLASTICS

1. THERMOPLASTICS are usually made from petroleum products. The most common are:
- Polyethylene terephthalate
- High-density polyethylene
- Polyvynyl chloride
- Low-density polyethylene
- Ploypropylene
- Moulded polystyrene
- Expanded polystyrene

2. THERMOSETTING PLASTICS are made from petroleum products. They include:
- Polyurethane
- Bakelite
- Melamine
- Polyester resins

3. Typical ELASTOMERS include rubber and neoprene.

KEY CONCEPTS OF PLASTIC MATERIALS

1. Plastics consist of long chains of atoms which are mostly composed of carbon.

2. Plastics can be classified into natural and synthetic.

3. The process of manufacturing plastic is called polymerisation.

4. Plastic materials are resistant, insulating, ductile, malleable, impermeable and light.

5. There are three types of plastic recycling processes: chemical and mechanical recycling and energy recovery.

8. ELECTRONICS (8.1)

Electronics involves the study of circuits that modify the intensity, direction or properties of electric currents.

8.1. ELECTRIC COMPONENTS

Here, we'll analyse the most common electronic components.

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 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 theorical 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
There are two types of resistances that depend on a physical factor:
  -Resistance that depends on temperature, that is called a thermistor. There are  two types of 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 ligth received.The resistance decreases as the amount of ligth increases. These devices ,like potentiometers, are often used in security systems, where they are parts of sensors.
Capacitors
A capcitor can store electrical energy from a battery and then use it to power a ligth bulb until the charge is totally depleted.
Capacitors are componets 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 (ligth emitting diode) only gives off ligth when an electric current flows through it.

7. ELECTROMAGNETIC CONTROL SYSTEMS

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

7.1. Cam switch controller

The device on the side of the pulley in the picture abovee is a cam. The shape of this device allows us to control the moment and duration of an activity.

 

7.2. Limit switches

There are two types of switches:

-Normally open
-Normally closed

6. ELECTROMAGNETIC MECHANISMS

These are devices that can convert movement into electricity or vice versa.

6.1. Electromagnetic generators

These generators transform mechanical energy into electricity. There are two types of generators:

Dynamos

It consists of a magnet and a rotary coil. The coil is located between the two poles of the magnet. The ends of the coil have two semicircular conductors, which form the commuttator. When electricity is applied to the coil, it rotates and begins to generate direct current in the coil.

  

Alternators

A simple alternator is almost identical to a dynamo, except the commutator, which consists of two metallic rings connected to carbon brushes.

6.2. 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.

 

 

6.3. Relays

It's an electromagnetic component that works such 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.

5. EFFECTS OF ELECTRIC CURRENT (5.3 + 5.4)

5.3. Electromagnetic effects

The following pictures show us how to create a magetic field with daily materials.

 

This effect can be used to pruduces movement, for example in electric motors.

To generate an electric current with a magnet, we can move the conductor or we can move the magnet. 

5.4. Sound

We can transform elecric current into sound by using diverse electromechanical devices, such as bells. Some of these devices are based on the piezoelectric effect.

5. EFFECTS OF ELECTRIC CURRENT ( 5.1 + 5.2)

The movement of electrons trhough conductive  materials produces effects that have useful applicattions.

5.1. 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

5.2.  Light

There are various ways that electricity can be used to produce light:

Incandescent bulbs

When an electric current passes trough the metalic filament of a light bulb, it produces light. This is called incandescense.

Fluorescents tubes

Inside a fluoreescent tube, there is a metallic filament, normally, made of tungsten. When an electric current passes trough the filament, electrons are emitted into the inert gas. These react with mercury, creating invisible, ultraviolet light. Then the phosphor coating inside the tube transforms the ultraviolet light into visible light.

Light-emitting diodes (LED)

A LED has layers of semiconductors materials. When the electricity is applied to it, the electrons and holes cross over into the active layer, where they combine and produce photons or particles of light.

4. TYPES OF CURRENT

4.1.Direct current

Between the terminals of a battery there is a continuous stable flow of energy. This is called direct current. In the same way if we connect a light bulb to a battery the electrons always flow in the same direction with the same current.

4.2.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.
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.



4.3.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:

V ef =V max / square root of 2

4.4. Transformers

There is an important difference between alternating and direct current. Alternating can be increased or decreased by a transformer. this allows us to transfer electrical energy at very high voltages and over hundred kilometres, without losing any of the energy as heat.

THEIR SYMBOL IS:

3. TYPES OF CIRCUITS

3.1. Series circuits

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

To calculate the total resistance of a circuit, we add the resistance values of each load:

RT = R1 + R2 + R3 ...

3.2. Parallel circuit

In a parallel circuit, the various components share the same input and output. In other words, the wires from both sides are joined together.

If identical batteries are connected in parallel, the voltage of the circuit won't increase. 

3.3. Combination circuit

A combination circuit has some elements connected in series, and some other 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 that are connected in parallel.

2. ELECTRICAL QUANTITIES

2.1. Voltage or potential difference

A light bulb uses energy from the electrons to produce light and heat.

The amount of energy that a generator can transfer to electrons depends on its voltage. This is measured in volts.

2.2. Measuring electric current

Electric current is the charge of electrons that flow through the cross-sections of a conductor every second.

Electric current is measured in amperes or amps in the International System or SI.

2.3. 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 throgh the material. This ratio, whic is called Ohm's Law, can be expressed as follows:

R = V / I

V = R x I

I = V / R

2.4. Electrical energy and power

Electrical energy

Electric energy is the energy that keeps the electrons of a circuit in motion. This energy is provided by a generator and consumed by one or more loads.

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 or kilowatts. One Kilowatts equals 1000 watts.

P = V x I

1. AN ELECTRIC CIRCUIT

An electric circuit is a pathway for the flow of electrons. It consists of different parts. Electric current is a continuous flow of electrons through a circuit.

1.1. Parts of an electric circuit

Electric circuits consists of various parts:

- Generators provide 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.

1.2. Diagrams and symbols

We use a system of conventional symbols to simplify the visual representation of electric and electronics circuits, making them easier to understand.

UNIT 7: ELECTRIC CIRCUITS AND ELECTRONICS

1.- An electric ciruit

2.- Electrical quantities

3.- Types of circuits

4.- Types of current

5.- Efects of electric current

6.- Electromagnetic mechanisms

7.- Electromagnetics control systems

8.- Electronics

7. ENVIRONMENTAL IMPACT

Power station have an important impact on local ecosystems.

7.1.Environmental impact assessment

Any proposed new technological project should include an environmental impact assessment.There should also be an assessment of the economic and social repercussions of the project before any important decisions are made. 

7.2. Effects on the environment

Extracting natural resources

Fossil fuels and radioactive elements , such as uranium, must be extracted from underground deposits.
Large areas of forest have been destroyed to provide wood for fuel.

Transporting fuel

Most oil is transported over land through pipelines and by sea in large ships called oil tankers.
Natural gas is transported over land through gas pipelines or bu sea in tankers as liquid natural gas (LNG).These tankers are call LNG carriers.

Generating electricity
Hydroelectric power stations require large amounts of water which must be stored behind dams in reservoirs.

Waste treatment

Filters can reduce pollutants , such as nitrous oxide and sulphur.
Low-sulphur coal can also be used to reduce sulphur emissions.
Large forests should be protected because they remove CO2 from the air.

Nuclear waste is kept in special containers with thick walls that block radiation.These containers are stored in nuclear graveyards,which are usually located underground or in deep ocean trenches.

7.3. CLIMATE CHANGE

Most of our electricity comes from power stations that use non renewable-energy sources.This situation has negative effects on the environment and the most serious is climate change a problem that is associated specifically with fossil fuels.

6.POWER STATIONS THAT USE RENEWABLE RESOURCES

6.1.Wind farms

Wind farms use the kinetic energy of the wind to generate electricity.The wind turns the blades of a turbine at the top of a tower.The blades are connected to a gearbox which increases the rotational speed of the generator.

The output and efficiency of a wind farm depend on two factors:
-the location of the farm,which determines the speed and strength of the winds.
-the number of turbines that can be installed there.

6.2.Hydroelectric power stations

Hydroelectric power stations use the energy of falling water to produce electricity.
There are two main types of hydroelectric power stations:

-In conventional hydroelectric stations,the water flows from the reservoir to the turbines through a high-pressure conduit.Then it flows out, usually into a river.

-In pumped-storage hydroelectric stations,the water flows from the turbines to a second reservoir.Then it is pumped back up to the higher reservoir and stored for later.These stations are often built in areas where there isn't enough rain or river water to keep the upper reservoir full, so the water must be reused.
 

Solar power stations use energy from sunlight to generate electricity.There are two types of solar power stations:solar thermal and photovoltaic.

6.3. Solar thermal stations

Solar thermal stations can use sunlight in two ways:
-With solar collectors that absorb sunlight in order to produce heat.
-With mirrors called heliostats that reflect and concentrate sunlight in one place.

Photovoltaic stations
In photovoltaic stations, solar pannels convert sunlight directly into electricity.Each panel contains many photovoltaic cells.
Small solar power installations can provide energy for homes and rural areas.Excess power can be stored in batteries or accumulators and used at night.

6.4.Biomass power stations 

Biomass is any organic material that is produced by natural processes.

There are many types of biomass which can be used to produce energy.
Plants materials can be composted and fermented in tanks called digesters.These processes convert biomass into fuel.

In a biomass power station the fuel used to produce energy comes from biomass.The steam produced from burning the biomass moves a turbine that is connected to a generator.

6.5.Marine power stations

Marine power stations use the movement of ocean water to generate elctricity.
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 surface of the ocean and deeper areas to produce energy.

6.6.Geothermal power stations 

Geothermal power stations use natural heat from the deepest underground layers of our planet.
Geothermal energy can be used in two ways:
-It can be use directly to provide hot water for heating and industrial uses.
-It can be used indirectly to drive generators and produce electricity.