test tiếng Anh ngành điện pptx

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test tiếng Anh ngành điện pptx

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Sample Midterm test Time allowed: 60 minutes Version A I - Read the following passage and choose the best answer The conversions of mechanical into electrical power and vice versa are one of the most important problems of electrical engineering. These conversions are made by means of electrical machines. When the machine is driven by mechanical torque, it converts mechanical energy into electrical energy and is called a generator, when it is driven electrically, by passing a current through it from some external source, it converts electrical energy into mechanical energy and is called a motor. A DC generator contains a field structure of an even number of poles mounted on a frame (which is a portion of the magnetic circuit and can act as a mechanical support for the machine as a whole). Upon them are wound field coils. A DC generator also includes an armature which rotates in the magnetic fields produced by the poles and is separated from the pole faces by the air gaps. When armature conductors are moved through the magnetic field, electromotive forces (e.m.f.s) are induced in them. These conductors are arranged in a winding in such a manner that certain groups of conductors are in series between two points of the winding. The electromotive force will be the greatest when the conductor is under a pole, and zero when the conductor is central between two poles. As the current flows from the external source through the armature conductors, they are in a magnetic field and are acted upon by forces all tending to turn the armature in one direction. Contact between the armature winding and the external circuit is through the brushes and the commutator. Brushes are fixed in comparison with the rotating armature, therefore the e.m.f. between them is constant and they transmit a constant voltage to the external circuit. The brushes are generally made of graphitized carbon. They fit into brush-holders and are held against the commutator by spring pressure. The commutator is composed of a number of copper segments insulated from each other. When a commutator segment passes under a brush, the current in the armature conductor connected with it must reverse from a given value in one direction to the same value in the opposite direction. This is known as commutation. DC motors have the same structure as DC generators. In other words, the field coils and armature windings used in motors are the same as in generators and the problem of commutation is also similar. 1. What kind of torque is a motor driven by? 2. What does the size of electromotive force depend on? A. The number of armature conductors in a DC motor. B. The position of the conductor in a DC generator. C. The number of armature conductors in a DC generator. D. The position of the conductor in a DC motor. 3. What separates the armature of a DC generator from the pole faces? A. poles B. field coils C. electromotive forces D. air gaps 4. What role do the brushes and commutator play in a DC generator? A. They fit into brush-holders and are held against the commutator by spring pressure. B. They get contact with the external circuit. C. They are able to turn the armature in one direction. D. They help to contact the armature winding with the external circuit 5. What is the next paragraph most probably about? A. Physical structure and operation of a DC motor. B. Possible applications of a DC generator. C. Make-up of a DC armature. D. Differences between a DC generator and an AC one. II - Give the proper term for each of the following definitions or explanations. Terms Definitions / Explanations 6 the path in which current moves from a point of high potential energy to one of low potential. 7 a device which converts mechanical energy into electrical energy 8. a material with many free electrons. 9. an instrument used to measure small currents 10. a device that is used to reduce heat 11 a circuit that has many paths for the current to flow 12. a device consisting two coils that can change voltages 13 a device which impedes the current flow in a circuit 14 a method of heating a non-conducting material, a dielectric, by high - frequency voltages. 15. a device which is used to rectify alternating current. III - Fill in each of the gaps with one suitable word. Semiconductors Semiconductor is a solid material (16) electrical conductivity at room temperature is between that of a conductor and that of an insulator. At (17) temperature, its conductivity approaches that of a metal, and at low temperature it acts as an insulator. In a semiconductor, there (18) a limited movement of electrons, depending (19) the crystal structure of the material used. The substances that were first used in semiconductors were elements such as germanium, and silicon. In their pure forms, both of them (20) properties close to insulators. It was found that the incorporation of certain impurities in them enhances (21) conductivity properties. The impurities either add free electrons (22) create holes in the crystal structures of the host substances by attracting electrons. Thus, there are (23) types of semiconductors: the N- type in which the current carriers are negative, and the P-type in (24) the positively- charged holes move and carry the current. Mixture of certain metallic oxides, known as thermistors, also acts as semiconductors. Their resistance falls rapidly as their temperature rises and vice versa. Therefore, they (25) used in temperature – sensing devices. IV - Joining the following groups of sentences to make longer sentences using suitable linking words. 26. Using a Time clause The current has reached a predetermined value. The relay contacts close. 27. Using a Relative Pronoun and Infinitive of Purpose Fluorescent lamps include a filter capacitor. The filter capacitor is fitted across the starter switch The filter capacitor prevents radio interference. 28. Using a Relative clause with Preposition The armature conductors are in a magnetic field and are acted upon by forces all tending to turn the armature in one direction. A current flows from the external source through these armature conductors. 29. Using a Linking word to express Qualification Mains supply are normally AC. For many applications a DC supply is required. 30. Using a Conditional clause The current rises sharply. The circuit breaker opens. V - Write sentences using the given words or phrases 31. Rectifier circuit / circuit / that / be / use / convert / alternating current / direct current. 32. Basic purpose / solar energy / be / to collect / solar radiation / and convert / it / useful thermal energy. 33. Electrons / collide / electrons of the argon and mercury vapour / tube, / causing / two gas / radiate ultraviolet light. 34. Resistor / be / sort / before / they / be / mark / indicate their values. 35. Commutator / consist / a number of copper segments / that / be / isolate / from one another. When / current / be / feed / field coils, / magnetic field / be / set up / stator. 21. Trivalent impurity / be / call / acceptor / because / it / accept / electron / crystal structure. Key FOR Sample Midterm test Version A I - 2 points for each correct answer ( 10 points ) 1. electrical 2. B 3. D 4. D 5. A II - 1 point for each correct answer ( 10 points ) 6. circuit 7. generator 8. conductor 9. miliammeter 10. heat sink 11. parallel circuit 12. transformer 13. resistor 14. dielectric heating 15. diode III- 1 point for each correct answer ( 10 points ) 16. a 17. high 18. is 19. on 20. have 21.their 22. or 23. two 24. which 25. are IV - 2 points for each correct answer (10 points) 26. When the current has reached a predetermined value, the relay contacts close. 27. Fluorescent lamps include a filter capacitor (that / which is ) fitted across the starter switch to prevent radio interference. 28. The armature conductors are in a magnetic field and are acted upon by forces all tending to turn the armature in one direction through which a current flows from the external source. 29. Although mains supplies are normally AC, for many applications a DC supply is required. Or Mains supply are normally AC, however / but for many applications a DC supply is required. 30. If the current rises sharply, the circuit breaker opens. V - 2 points for each correct answer ( 10 points ) 31. A rectifier circuit is a circuit that is used to convert an alternating current into a direct current. 32. The basic purpose of solar energy is to collect solar radiation and convert it into useful thermal energy. 33. Electrons collide with electrons of the argon and mercury vapour in the tube, causing the two gases to radiate ultraviolet light. 34. Resistors are sorted before they are marked to indicate their values. 35.A commutator consists of a number of copper segments that is isolated from one another. Total score: 50 points Sample Midterm test Time allowed: 60 minutes Version B I - Read the following passage and choose the best answer The conversions of mechanical into electrical power and vice versa are one of the most important problems of electrical engineering. These conversions are made by means of electrical machines. When the machine is driven by mechanical torque, it converts mechanical energy into electrical energy and is called a generator, when it is driven electrically, by passing a current through it from some external source, it converts electrical energy into mechanical energy and is called a motor. A DC generator contains a field structure of an even number of poles mounted on a frame (which is a portion of the magnetic circuit and can act as a mechanical support for the machine as a whole). Upon them are wound field coils. A DC generator also includes an armature which rotates in the magnetic fields produced by the poles and is separated from the pole faces by the air gaps. When armature conductors are moved through the magnetic field, electromotive forces (e.m.f.s) are induced in them. These conductors are arranged in a winding in such a manner that certain groups of conductors are in series between two points of the winding. The electromotive force will be the greatest when the conductor is under a pole, and zero when the conductor is central between two poles. As the current flows from the external source through the armature conductors, they are in a magnetic field and are acted upon by forces all tending to turn the armature in one direction. Contact between the armature winding and the external circuit is through the brushes and the commutator. Brushes are fixed in comparison with the rotating armature, therefore the e.m.f. between them is constant and they transmit a constant voltage to the external circuit. The brushes are generally made of graphitized carbon. They fit into brush-holders and are held against the commutator by spring pressure. The commutator is composed of a number of copper segments insulated from each other. When a commutator segment passes under a brush, the current in the armature conductor connected with it must reverse from a given value in one direction to the same value in the opposite direction. This is known as commutation. DC motors have the same structure as DC generators. In other words, the field coils and armature windings used in motors are the same as in generators and the problem of commutation is also similar. 1. An electrical machine driven mechanically is called 2. What are field coils wound on? A. frame B. poles C. magnetic circuit D. mechanical support 3. Which of the following statements about the frame of a DC generator is True? A. It is a part of the mechanical circuit and a magnetic support for the machine. B. It is a mechanical circuit and a part of the magnetic support for the machine. C. It is a part of the magnetic circuit and a mechanical support for the machine. D. It consists of a magnetic circuit and a mechanical support for the machine. 4. How does the armature winding contact the external circuit? A. through the brushes and the commutator C. by the magnetic field B. through the armature conductors D. by the pole faces. 5. What is the function of air gaps in a DC generator? A. To rotate an armature of the DC generator in the magnetic fields. B. To produce the magnetic field in the poles. C. To separate an armature from the pole faces. D. To make poles separate from the pole faces. II-Give the proper term for each of the following definitions or explanations Terms Definitions / Explanations 6. a closed path around which a current can flow. 7. a type of plants that combine the generation of electricity and heat using solar power, fossil fuels, syngas, biomass, or biogas as a fuel source. 8. a material with very few, if any, electrons 9. an instrument used to measure huge resistance 10. a device that is used to select a frequency. 11. an electronic component for opening and closing a circuit 12. the process in which a chemical compound is separated into its components by an electric current. 13. a device which obstructs the current flow in a circuit 14. a process in which an ionized gas is made to cut a magnetic field to generate electricity. 15. an electronic device for receiving signals III - Fill in each of the gaps with one suitable word Capacitors A capacitor is a device which is used (16) oppose any change in circuit voltage. The capacitor property of opposition against voltage change is (17) as capacitance. Capacitors are made to store electric energy. This (18) electricity is known as electric potential difference, or an electrostatic field with several electrons in it. When the build-up of electrons becomes great (19) , the electric potential is discharged. In its simple make-up, a capacitor is composed of two plates of a conductor material, (20) are isolated from one another, and between them is a dielectric material. The dielectric does not (21) electrons pass through it easily. The capacitance of a capacitor is determined by the thickness of the (22) materials. The electrons are stored on the plate surfaces. Therefore , the size of the plate is directly (23) to the degree of capacitance. When a voltage is applied to the plates of a capacitor, potential difference is created. This caused electrons to be transferred from the positive plate to the (24) one. The transfer continues as long as the voltage source is (25) to the two plates and until the accumulated charge become equal to the potential difference of the applied voltage. IV - Joining the following groups of sentences to make longer sentences using suitable linking words 26. Using a Time clause The current flows through the coil. Both fixed and turning vanes are magnetized and so resist each other. 27. Using a Relative clause with Preposition Secondary cells are devices. The material of the electrodes and the products of the chemical reaction are substantially insoluble in the electrolyte in these devices. 28. Using a linking word to express Qualification Heat is sometimes undesirable and has to be reduced. Domestic appliances such as electric cookers and many industrial processes depend on the heating effect of an electric current. 29. Using a Relative clause The error sensor output is fed to the controller. This controller sends a signal to the power supply of the motor. 30. Using a Conditional clause The temperature is increased. The kinetic energy of the electrons rises and more electrons escapes. V - Write sentences using the given words or phrases. 31. Cell / be / device / that / convert / chemical energy / electricity. 32. Tracking collector / be / control / follow / sun throughout the day. 33. Filament electrodes / heat / causing / stream of electrons / flow / between the filament electrodes. 34. Ideally, / switch / offer / zero impedance / current / when / be / close. 35. Although / function / satellite circuit / much complex / than that of the flashlight, / it / consist / four basic element / : source, transmission system, load and control. Key FOR Sample Midterm test Version B I - 2 points for each correct answer ( 10 points ) 1.generator 2. B 3.C 4.D 5. C II - 1 point for each correct answer ( 10 points ) 6. circuit 7. co-generation plant 8. insulator 9. megohmmeter 10. variable capacitor 11. switch 12. electrolysis 13. resistor 14. MHD generation 15. ANTENNA/ aerial III- 1 point for each correct answer ( 10 points ) 16. to 17. known 18. stored 19. enough 20. which 21. let 22. dielectric 23. proportional 24. negative 25. equal IV - 2 points for each correct answer ( 10 points ) 26. When the current flows through the coil, both fixed and turning vanes are magnetized and so resist each other. 27. Secondary cells are devices in which the material of the electrodes and the products of the chemical reaction are substantially insoluble in the electrolyte. 28. Although heat is sometimes undesirable and has to be reduced, domestic appliances such as electric cookers and many industrial processes depend on the heating effect of an electric current. Or Heat is sometimes undesirable and has to be reduced, however / but domestic appliances such as electric cookers and many industrial processes depend on the heating effect of an electric current. 29. The error sensor output is fed to the controller which / that sends / sending a signal to the power supply of the motor. 30. If the temperature is increased, the kinetic energy of the electrons rises and more electrons escapes. V - 2 points for each correct answer ( 10 points ) 31. A cell is a device that converts chemical energy into electricity. 32. Tracking collectors are controlled to follow the sun throughout the day. 33. Filament electrodes heat, causing a / the stream of electrons to flow between the filament electrodes. 34. Ideally, a switch offers zero impedance to currents when it is closed. 35. Although the function of a satellite circuit is much more complex than that of the flashlight, it consists of four basic elements : source, transmission system, load and control. Total score: 50 points . Sample Midterm test Time allowed: 60 minutes Version A I - Read the following passage and choose the best answer The. conductors are in series between two points of the winding. The electromotive force will be the greatest when the conductor is under a pole, and zero when the conductor is central between two poles call / acceptor / because / it / accept / electron / crystal structure. Key FOR Sample Midterm test Version A I - 2 points for each correct answer ( 10 points ) 1. electrical 2. B 3. D 4. D 5.

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  • Semiconductors

  • Capacitors

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