2016年称英语理工类概括大意专项练习.docVIP

2016年职称英语理工类概括大意专项练习 Maglev Trains 　　1　A few countries are using powerful electromagnets to develop high-speed trains, called maglev trains. Maglev is short for magnetic levitation 1 , which means that these trains float over a guide way using the basic principles of magnets to replace the old steel wheel and track trains. 　　2 If youve ever played with magnets, you know that opposite poles attract and like poles repel each other2. This is the basic principle behind electromagnetic propulsion. Electromagnets are similar to other magnets in that they attract metal objects, but the magnetic pull is temporary. You can easily create a small electromagnet yourself by connecting the ends of a copper wire to the positive and negative ends of an AA-cell battery3. This creates a small magnetic field. If you disconnect either end of the wire from the battery, the magnetic field is taken away. 　　3　The magnetic field created in this wire-and-battery experiment is the simple idea behind a　maglev train rail system. There are three components to this system: A large electrical power　source, metal coils lining a guide way or track, and large guidance magnets attached to the　underside of the train. 　　4　The big difference between a maglev train and a conventional train is that maglev trains do not have an engine -- at least not the kind of engine used to pull typical train cars along steel tracks4. The engine for maglev trains is rather innoticeable. Instead of using fossil fuels, the magnetic field created by the electrified coils in the guideway walls and the track combines to propel the trains5. 　　5　The magnetized coil running along the track, called a guideway, repels the large magnets on the trains undercarriage, allowing the train to levitate between 1 to 10 cm above the guideway. Once the train is levitated, power is supplied to the coils within the guideway walls to create a unique system of magnetic fields that pull and push~ th train along the guideway. The electric curren