III. Write the summary of the Text 4.
IV. Scan the table and find a material which is:
1) soft
2) ductile
3) malleable
4) tough
5) scratch-resistant
6) conductive and malleable
7) durable and hard
8) stiff and brittle
9) ductile and corrosion resistant
10) heat resistant and chemical resistant
| Materials | Properties | Uses |
| Metals | ||
| Aluminium | Light, soft, ductile, highly conductive, corrosion-resistant | Aircraft, engine components, foil, cooking utensils |
| Copper | Very malleable, tough and ductile, highly conductive, corrosion-resistant | Electric wiring, PCBs, tubing |
| Brass (65 % copper, 35 % zinc) | Very corrosion-resistant. Casts well, easily machined. Can be work hardened. Good conductor. | Valves, taps, castings, ship fittings, electrical contacts |
| Mild steel (iron with 0.15% to 0.3% carbon) | High strength, ductile, tough, fairly malleable. Cannot be hardened and tempered. Low cost. Poor corrosion resistance. | General purpose |
| High carbon steel (iron with 0.7% to 1.4% carbon) | Hardest of the carbon steels but less ductile and malleable. Can be hardened and tempered. | Cutting tools such as drills, files, saws |
| Thermoplastics | ||
| ABS | High impact strength and toughness, scratch-resistant, light and durable. | Safety helmets, car components, telephones, kitchenware |
| Acrylic | Stiff, hard, very durable, clear, can be polished easily. Can be formed easily. | Aircraft canopies, baths, double glazing |
| Nylon | Hard, tough, wear-resistant, self lubricating | Bearings, gears, casings for power tools |
| Thermosetting plastics | ||
| Epoxy resin | High strength when reinforced, good chemical and wear resistance. | Adhesives, encapsulation of electronic components |
| Polyester resin | Stiff, hard, brittle. Good chemical and heat resistance. | Moulding, boat and car bodies |
| Urea formaldehyde | Stiff, hard, strong, brittle, heat-resistant, and a good electrical insulator. | Electrical fittings, adhesives |
V. Scan the table to find:
1. A metal used to make aircraft
2. Plastics used for adhesives
3. Steel which can be hardened
4. An alloy suitable for castings
5. A plastic with very low friction
6. A material suitable for safety helmets
7. A metal suitable for a salt-water environment
8. A metal for general construction use but which should be protected from corrosion
9. A plastic for car bodies
10. The metal used for the conductors in printed circuit boards
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VI. Make definitions of each of the materials in column A, choosing the correct information in columns B and C.
| A | B | C |
| 1. An alloy 2. A thermoplastic 3. Mild steel 4. A conductor 5. An insulator 6. High carbon steel 7. Brass 8. A thermosetting plastic | a metal a material an alloy | allows heat or current to flow easily. remains rigid at high temperatures. does not allow heat or current to flow easily. contains iron and 0,7 % to 1,4 % carbon. becomes plastic when heated. contains iron and 0,15 % to 0, 3 % carbon. formed by mixing other metals. consists of copper and zinc. |
Text 5.
I. Read the statements given below and if you think the statement is true agree to it saying “That’s right”. If you think it is not true, disagree “That’s wrong” and make the necessary corrections.
a. Electrodynamic suspension train is a type of a maglev train.
b. The construction of maglev trains doesn’t have wheels.
c. The drag force is always a negative factor for a vehicle.
d. Electrodynamic suspension system has definite disadvantages as every technical system.
e. Maglev train systems are widely spread all over the world.
II. Read the text and say if you are right or wrong.
Vocabulary
to levitate ['levɪteɪt] – поднимать(ся)
repulsive [rɪ'pʌlsɪv] – отталкивающий
array [ə'reɪ] – набор, комплект
minor ['maɪnə] – незначительный
gap [gæp] – промежуток; зазор
separation [,sep(ə)'reɪʃ(ə)n] – интервал, расстояние
flux [flʌks] – поток
to sustain [sə'steɪn] – поддерживать, способствовать
drag [dræg] – помеха; тормоз
offset ['ɔfset] – контраст
Electrodynamic Suspension System
In electrodynamic suspension (EDS), both the rail and the train exert a magnetic field, and the train is levitated by the repulsive force between these magnetic fields. The magnetic field in the train is produced by either superconducting magnets or by an array of permanent magnets. The repulsive force in the track is created by an induced magnetic field in wires or other conducting lines in the track (Fig. 1). A major advantage of the repulsive maglev systems is that they are naturally stable – a minor air gap between the track and the magnets creates strong forces to repel the magnets back to their original position, while a slight increase in distance greatly reduces the force and again returns the vehicle to the right separation. No feedback control is needed.
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Repulsive systems have a major disadvantage as well. At slow speeds, the current induced in these coils and the resultant magnetic flux is not large enough to support the weight of the train. For this reason the train must have wheels or some other form of chassis to support the train until it reaches a speed that can sustain levitation. Since a train may stop at any location, due to equipment problems for instance, the entire track must be able to support both low-speed and high-speed operation. Another disadvantage is that the repulsive system naturally creates a field in the track in front and to the rear of the lift magnets, which act against the magnets and create a form of drag. This is generally only a concern at low speeds; at higher speeds the effect does not have time to build to its full potential and other forms of drag dominate.
Fig.1 Fig. 2
The drag force can be used to the electrodynamic system's advantage, however, as it creates a varying force in the rails that can be used as a reactionary system to drive the train, without the need for a separate reaction plate, as in most linear motor systems. Alternatively, propulsion coils on the guideway are used to exert a force on the magnets in the train and make the train move forward. The propulsion coils that exert a force on the train are effectively a linear motor: an alternating current flowing through the coils generates a continuously varying magnetic field that moves forward along the track. The frequency of the alternating current is synchronized to match the speed of the train. The offset between the field exerted by magnets on the train and the applied field creates a force moving the train forward (Fig. 2).
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III. Answer the following questions:
1. What operating principle is the electrodynamic suspension system based on?
2. What is the main advantage of the electrodynamic suspension system?
3. What disadvantages does the repulsive maglev train have?
4. Why does the drag force appear?
5. How can the drag force set in motion the train?
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