test tiếng Anh ngành điện pptx

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 thro

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

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

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 nonconducting 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-N-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 )

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

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

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

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

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 )

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