3. PLASTICS AND TEXTILES.

3. Plastics and textiles.

Keys Concepts.

1. Plastic materials.

• Plastics consist of long chains of atoms which are mostly composed of carbon. 
• Plastics can be classified into natural and syhnthetic plastics.
• The process of manufacturing plastic is called polymerisation.
• There are three types of plastic recycling processes: chemical and mechanical recycling and energy recovery. 

2. The classification by internal structure.

• Thermoplastics are usually madre from petroleum products. The most common thermoplastics are: polyethylene terephthalate, high-density polyethylene, polyvinyl chloride, 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 include rubber and neoprene. 

 3. Plastic forming techniques.

• Various industrial techniques can be used to manufactures 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.

4. Modification techniques.

•  Modification techniques use tools and machines to make changes to prefabricated materials, such as sheets, bars or mouldings.

5. Textiles.

• Both natural and synthetic fibres can be oven 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.

 

8. ELECTRONS

 8.1. 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.





Variable resistance or ptentiometer.
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 factors that effect resistance may be temperature or the amount of light:
  -Resistance that depends on temperature 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 light received. The resistance decreases as the amount of light increases.

Capacitors.
A capacitor can store electrical energy from a battery and then use it to power a light bulb until the charge is totally depleted.
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. A diode has two electrodes: an anode (A) and a cathode (K).
A LED only gives off light when an electric current flows throught it.

Transistors.
They are made from semiconductor materials and have three electrodes called the base, the collector and the emitter.
There are two types of transistor: NPN and PNP.

• When no electrons are flowing through the base, then no electrons can pass from the collector to the emitter. 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 saturations levels, it will be proportional to th flow of electrons between the collector and the emitter. The transistor is in the active region.

8.2. Basic devices made with eletronic components.
Timers.
A timer is a device that operates for a cetain period of time and then shuuts itself off automatically.
Integrated circuits.
Integrated circuits consist of miniature electronic components, such as transistors, resistors and capacitors.

7. ELECTROMAGNETIC CONTROL SYSTEMS.

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 above is called a cam.

7.2. Limit switches.
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.

Normally closed (N/C)
It opens when it is activated.

Normally open (N/O)
It closes when it is activated.

6. ELECTROMAGNETIC MECHANISMS.

6. ELECTROMAGNETIC MECHANISMS.

They use electromagnetic phenomena to produce electricity or convert it into mechanical energy.

6.1. Electromagnetic generators.

Generators 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 coil is located beteen the two poles of the magnet. The ends of the coil have two semi-circular conductors, which form the commutator.

Alternators.
A simple alternator is almost identical to a dynamo, except for the commutador, which consist of two metallic rings connected to carbon brushes. Instead of a direct current, this produces alternating current.

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.
A relay is an electromagnetic component that works as a switch. Relays may have a single circuit with one moveable contact. 

5. EFFECTS OF ELECTRIC CURRENT

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.
Incandescent bulbs.
When an electric current passes through the metallic filament of a lightbulbs, it produces light. This phenomenon is called incandescence.

Fluorescent tubes.
Inside a fluorescent tube, there is a metallic filament, normally of tungsten. 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.

5.3. Electromagnetic effects.
In this experiment, the electric circuit has created a magnetic field. This effect can be used to produce movement.

5.4. 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 piezoelectric effect.

4. TYPES OF CURRENT

4.1. Direct current.
Between the terminals of a battery, there is a continuous, stable flow of energy. If we use a voltmeter to measure the current in a car battery, the result will always be 12 volts. This is called direct current.

4.2. Alternating current.
If we measured the voltage of an electrical socket, the results could be represented in a graph like the one below:

• The current begins at 0 V and increases to 325 V.
• The current decreases from 325 V to 0 V.
• The current becomes negative and decreases to -325 V.
• The current increases to 0 V.

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.

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:
                                                            Vef = Vmax/√2
4.4. Transformers.
Transformers consist of two windings made of copper wire. If we apply an alternating current to one of them, it will produce a certain voltage in the other. The value will depend on the number of times that the copper wire has been wrapped around each winding, represented as n1 and n2:
                                                           V1/V2 = n1/n2

3. TYPES OF CIRCUITS

3.1. Series circuit.

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:
                                                      R = R1 + R2 + R3 +...
One example of this type of connection would be a series of generators.
In other words:                             V = V1 + V2 + V3 +...
 

3.2. Parallel circuit.
If identical batteries are connected in parallel, the voltage of the circuit will not increase.
The equivalent resistance of this type of circuit would be:
                                                    1/R = 1/R1 + 1/R2 + 1/R3 +...
 

3.3. Combination circuit.
A combination circuit has some elements connected in series and other elements connected in parallel.