电气技术专业英语电气技术专业英语

朱一纶 主编朱一纶 主编

中国电力出版社中国电力出版社

Unit 2 Basic ComponentsUnit 2 Basic Components

课件制作课件制作 : : 吴岱曦吴岱曦

IndexIndex

• TextText– 1. Resistor 1. Resistor – 2. Capacitor2. Capacitor

– 3. Inductor 3. Inductor

– 4. Impedance4. Impedance

• Reading materialsReading materials– 1. Resistor Color Codes 1. Resistor Color Codes – 2. Domestic power plugs and sockets 2. Domestic power plugs and sockets – 3. Battery charger3. Battery charger

• ExercisesExercises– 1. Put the Phrases into English 1. Put the Phrases into English – 2. Put the Phrases into Chinese 2. Put the Phrases into Chinese – 3. Sentence Translation3. Sentence Translation– 4. 4. TranslationTranslation

TextText

1. Resistor1. Resistor

• Suppose that some material is Suppose that some material is connected to the terminals of an connected to the terminals of an ideal voltage source as shown in ideal voltage source as shown in Fig2.1(a),if the resulting currentFig2.1(a),if the resulting current i(t) i(t) is always directly proportional to the is always directly proportional to the voltage for any function voltage for any function v(t)v(t), then the , then the material is called a linear resistor, or material is called a linear resistor, or resistor for short. resistor for short.

Fig 2.1 the relationship of voltage and Fig 2.1 the relationship of voltage and currentcurrent

(a)(a) Connected circuitConnected circuit(b)(b) i(t)i(t) is directly proportional to is directly proportional to v(t)v(t)

• Since voltage and current are directly Since voltage and current are directly proportional for a resistor, there exists a proportional for a resistor, there exists a proportionality constant R, called proportionality constant R, called resistance.resistance.

• The amount of current flowing in a resistor is dThe amount of current flowing in a resistor is directly proportional to the voltage across it anirectly proportional to the voltage across it and inversely proportional to the resistance of thd inversely proportional to the resistance of the resistor. This is Ohm law and can be expresse resistor. This is Ohm law and can be expressed as a formula:ed as a formula: v(t)v(t)==Ri(t)Ri(t)

• The units of resistance (volts per The units of resistance (volts per ampere) are referred to as ohms, ampere) are referred to as ohms, and are denoted by the capital Greek and are denoted by the capital Greek letter omega, Ω. A plot of voltage letter omega, Ω. A plot of voltage versus current for a (linear) resistor versus current for a (linear) resistor is given in Fig 2.1(b).is given in Fig 2.1(b).

• Resistors are used to limit current Resistors are used to limit current flowing to a device, thereby flowing to a device, thereby preventing it from burning out, as preventing it from burning out, as voltage dividers to reduce voltage for voltage dividers to reduce voltage for other device, as transistor biasing other device, as transistor biasing circuits, and to serve as circuit loads. circuits, and to serve as circuit loads.

• Fig2.2 (a) shows the different resistor Fig2.2 (a) shows the different resistor symbols that are used in circuit symbols that are used in circuit diagrams. The rectangular box is diagrams. The rectangular box is used throughout Europe, while the used throughout Europe, while the zig-zag line is more common in Japan zig-zag line is more common in Japan and the USA. and the USA.

Fig 2.2 Resistors Fig 2.2 Resistors

2. Capacitor2. Capacitor

• A capacitor is an electronic device for A capacitor is an electronic device for temporarily store electrical energy. temporarily store electrical energy. Capacitors can be found in almost Capacitors can be found in almost any complex electronic circuit. There any complex electronic circuit. There are many different types of capacitor are many different types of capacitor but they all work in essentially the but they all work in essentially the same way. same way.

• A simplified view of a capacitor is a A simplified view of a capacitor is a pair of metal plates separated by a pair of metal plates separated by a gap in which there is an insulating gap in which there is an insulating material known as the dielectric. This material known as the dielectric. This simplified capacitor is also chosen as simplified capacitor is also chosen as the electronic circuit symbol for a the electronic circuit symbol for a capacitor is a pair of parallel plates capacitor is a pair of parallel plates as shown in Fig2.3(a). as shown in Fig2.3(a).

• Some capacitors’ capacitance can be Some capacitors’ capacitance can be adjusted, so they are variable adjusted, so they are variable capacitors (Fig 2.3(b)). capacitors (Fig 2.3(b)).

Fig 2.3 capacitors Fig 2.3 capacitors

• If voltage is applied to the capacitor If voltage is applied to the capacitor terminals, charge flows in and terminals, charge flows in and collects on one plate. Meanwhile, collects on one plate. Meanwhile, current flows out of the other current flows out of the other terminal, and a charge of opposite terminal, and a charge of opposite polarity collects on the other plate. polarity collects on the other plate.

• The magnitude of the net charge Q The magnitude of the net charge Q on one plate is proportional to the on one plate is proportional to the applied voltage V. Thus, we have applied voltage V. Thus, we have Q=CVQ=CV, in which C is the capacitance., in which C is the capacitance.

• A capacitor will block dc current, but apA capacitor will block dc current, but appears to pass ac current by charging and pears to pass ac current by charging and discharging. It develops an ac resistance,discharging. It develops an ac resistance, known as capacitive reactance, which is known as capacitive reactance, which is affected by the capacitance and ac frequaffected by the capacitance and ac frequency. The formula for capacitive reactanency. The formula for capacitive reactance is ce is XC=1/(2πfC C)XC=1/(2πfC C), with units of ohms, with units of ohmsΩΩ. .

3. Inductor3. Inductor

• An inductor is an electrical device, An inductor is an electrical device, which can temporarily store which can temporarily store electromagnetic energy in the field electromagnetic energy in the field about it as long as current is flowing about it as long as current is flowing through it. The inductor is a coil of through it. The inductor is a coil of wire that may have an air core or an wire that may have an air core or an iron core to increase its inductance. iron core to increase its inductance.

• The circuit symbols for inductors are shoThe circuit symbols for inductors are shown in Fig 2.4(a). wn in Fig 2.4(a). Some inductors’ Some inductors’ inductance can be adjusted; inductance can be adjusted; a powerea powered iron core in the shape of a cylinder mad iron core in the shape of a cylinder may be adjusted in and out of the corey be adjusted in and out of the core in in such inductorssuch inductors, , so they are variable so they are variable inductors .inductors .

Fig 2.4 inductors Fig 2.4 inductors

• An inductor tends to oppose a change An inductor tends to oppose a change in electrical current, it has no resistance in electrical current, it has no resistance to dc current but has an ac resistance to dc current but has an ac resistance to ac current, known as inductive to ac current, known as inductive reactance, this inductive reactance is reactance, this inductive reactance is affected by inductance and the ac affected by inductance and the ac frequency and is given by the formula frequency and is given by the formula XXLL=2πf=2πfLL L L, with units of ohms. , with units of ohms.

4. Impedance4. Impedance

• Impedance (symbol Z) is a measure of thImpedance (symbol Z) is a measure of the overall opposition of a circuit to currene overall opposition of a circuit to current, in other words: how much the circuit it, in other words: how much the circuit impedes the flow of current. It is like resimpedes the flow of current. It is like resistance, but it also takes into account the stance, but it also takes into account the effects of capacitance and inductance. Ieffects of capacitance and inductance. Impedance is measured in ohms, symbol mpedance is measured in ohms, symbol ΩΩ. .

• Impedance is more complex than Impedance is more complex than resistance because the effects of resistance because the effects of capacitance and inductance vary capacitance and inductance vary with the frequency of the current with the frequency of the current passing through the circuit and this passing through the circuit and this means impedance varies with means impedance varies with frequency! The effect of resistance is frequency! The effect of resistance is constant regardless of frequency. constant regardless of frequency.

• The term 'impedance' is often used for The term 'impedance' is often used for simple circuits which have no simple circuits which have no capacitance or inductance - for capacitance or inductance - for example to refer to their example to refer to their 'input impedance' or 'input impedance' or 'output impedance'. This can seem 'output impedance'. This can seem confusing if you are learning confusing if you are learning electronics, but for these simple electronics, but for these simple circuits you can assume that it is just circuits you can assume that it is just another word for resistance. another word for resistance.

• Four electrical quantities determine the Four electrical quantities determine the impedance (Z) of a circuit: resistance (R), impedance (Z) of a circuit: resistance (R), capacitance (C), inductance (L) and freqcapacitance (C), inductance (L) and frequency (f). uency (f).

• Impedance can be split into two parts: Impedance can be split into two parts: ZZ=R+jX=R+jX

• Resistance R (the part which is Resistance R (the part which is constant regardless of frequency).constant regardless of frequency).

• Reactance X (the part which varies Reactance X (the part which varies with frequency due to capacitance with frequency due to capacitance and inductance). and inductance).

This is the End of the TextThis is the End of the Text

Reading materialsReading materials

1. Resistor Color Codes1. Resistor Color Codes

• Components are coded with colors to idComponents are coded with colors to identify their value and toleranceentify their value and tolerance ，， here there takes the resistor as an example.akes the resistor as an example.

• The values of the resistor are calculated The values of the resistor are calculated from the color of the bands (see Tab 2.1) from the color of the bands (see Tab 2.1) . The values of the colors are shown in T. The values of the colors are shown in Table able 2.12.1. The first band is the tens value. The first band is the tens values. The second band gives the units; the ts. The second band gives the units; the third band is a multiplying factor, the facthird band is a multiplying factor, the factor being 10’s band value. or being 10’s band value.

• The fourth band gives the tolerance The fourth band gives the tolerance of the resistor. No band implies a of the resistor. No band implies a tolerance of ± 20%, a silver band tolerance of ± 20%, a silver band means the resistor has a tolerance of means the resistor has a tolerance of ± 10% and a gold band has the ± 10% and a gold band has the closest tolerance of ± 5%. closest tolerance of ± 5%.

• For a For a 5-band resistor, the first band is th5-band resistor, the first band is the hundreds values. The second band give hundreds values. The second band gives the tens and the third band gives unites the tens and the third band gives unitss.. The forth band is a multiplying factor, The forth band is a multiplying factor, the factor being 10’s band value. the factor being 10’s band value.

• The colors brown, red, green, blue, The colors brown, red, green, blue, and violet are used as tolerance and violet are used as tolerance codes on 5-band resistors only. All 5-codes on 5-band resistors only. All 5-band resistors use a colored band resistors use a colored tolerance band.tolerance band.

Table 2.1 Table 2.1 The values of the colorThe values of the colors s

Fig 2.5 Resistor Color Codes Fig 2.5 Resistor Color Codes

• Fig 2.6 gives some examples of color code Fig 2.6 gives some examples of color code resistor. Resistor in Fig 2.6(a) colored resistor. Resistor in Fig 2.6(a) colored Brown-Green-Grey-Silver-Red would be Brown-Green-Grey-Silver-Red would be 1.58 Ω with a tolerance of ± 2% 1.58 Ω with a tolerance of ± 2%

• resistor in Fig 2.6(b) colored Yellow-Violet-resistor in Fig 2.6(b) colored Yellow-Violet-Orange-Gold would be 47 kΩ with a toleraOrange-Gold would be 47 kΩ with a tolerance of ± 5%. nce of ± 5%.

2. Domestic power plugs 2. Domestic power plugs and socketsand sockets

• In most countries, household power In most countries, household power is single-phase electric power, in is single-phase electric power, in which a single phase conductor which a single phase conductor brings alternating current into a brings alternating current into a house, and a neutral returns it to the house, and a neutral returns it to the power supply. power supply.

• Domestic power plugs and sockets Domestic power plugs and sockets (Fig 2.7) are devices that connect the (Fig 2.7) are devices that connect the home appliances and portable light home appliances and portable light fixtures commonly used in homes to fixtures commonly used in homes to the commercial power supply so that the commercial power supply so that electric power can flow to them. electric power can flow to them.

• Many plugs and sockets include a Many plugs and sockets include a third contact used for a protective third contact used for a protective earth ground, which only carries earth ground, which only carries current in case of a fault in the current in case of a fault in the connected equipment. connected equipment.

• Power plugs are male electrical Power plugs are male electrical connectors that fit into female connectors that fit into female electrical sockets. They have electrical sockets. They have contacts that are pins or blades that contacts that are pins or blades that connect mechanically and electrically connect mechanically and electrically to holes or slots in the socket. to holes or slots in the socket.

• Plugs usually have a phase or hot Plugs usually have a phase or hot contact, a neutral contact, and an contact, a neutral contact, and an optional earth or Ground contact. Many optional earth or Ground contact. Many plugs make no distinction between the plugs make no distinction between the live and neutral contacts, and in some live and neutral contacts, and in some cases they have two live contacts. The cases they have two live contacts. The contacts may be steel or brass, either contacts may be steel or brass, either zinc, tin or nickel plated. zinc, tin or nickel plated.

• Power sockets are female electrical Power sockets are female electrical connectors that have slots or holes connectors that have slots or holes which accept the pins or blades of which accept the pins or blades of power plugs inserted into them and power plugs inserted into them and deliver electricity to the plugs. deliver electricity to the plugs.

• Sockets are usually designed to reject aSockets are usually designed to reject any plug which is not built to the same elny plug which is not built to the same electrical standard. Some sockets have onectrical standard. Some sockets have one or more holes that connect to pins on te or more holes that connect to pins on the plug. he plug.

Fig Fig 2.7 Domestic power 2.7 Domestic power Various Plugs & Sockets Various Plugs & Sockets

3. Battery charger3. Battery charger

• A battery charger is a device used to A battery charger is a device used to put energy into a secondary cell or put energy into a secondary cell or (rechargeable) battery by forcing an (rechargeable) battery by forcing an electric current through it. electric current through it.

• The charge current depends upon The charge current depends upon the technology and capacity of the the technology and capacity of the battery being charged. For example, battery being charged. For example, the current that should be applied to the current that should be applied to recharge a 12 V car battery will be recharge a 12 V car battery will be very different from the current for a very different from the current for a mobile phone battery.mobile phone battery.

• A simple charger works by A simple charger works by connecting a constant DC power connecting a constant DC power source to the battery being charged. source to the battery being charged. The simple charger does not alter its The simple charger does not alter its output based on time or the charge output based on time or the charge on the battery. This simplicity means on the battery. This simplicity means that a simple charger is inexpensive, that a simple charger is inexpensive, but there is a tradeoff in quality. but there is a tradeoff in quality.

• Typically, a simple charger takes Typically, a simple charger takes longer to charge a battery to prevent longer to charge a battery to prevent severe over-charging. Even so, a severe over-charging. Even so, a battery left in a simple charger for battery left in a simple charger for too long will be weakened or too long will be weakened or destroyed due to over-charging. destroyed due to over-charging.

• A trickle charger is a kind of simple A trickle charger is a kind of simple charger that charges the battery charger that charges the battery slowly, at the self-discharge rate. A slowly, at the self-discharge rate. A trickle charger is the slowest kind of trickle charger is the slowest kind of battery charger. Leaving a battery in battery charger. Leaving a battery in a trickle charger keeps the battery a trickle charger keeps the battery "topped up" but never over-charges."topped up" but never over-charges.

• The output of a timer charger is The output of a timer charger is terminated after a pre-determined terminated after a pre-determined time. Timer chargers were the most time. Timer chargers were the most common type for high-capacity Ni-Cd common type for high-capacity Ni-Cd cells in the late 1990s.Often a timer cells in the late 1990s.Often a timer charger and set of batteries could be charger and set of batteries could be bought as a bundle and the charger bought as a bundle and the charger time was set to suit those batteries. time was set to suit those batteries.

• If batteries of lower capacity were If batteries of lower capacity were charged then they would be charged then they would be overcharged, and if batteries of overcharged, and if batteries of higher capacity were charged they higher capacity were charged they would be only partly charged. would be only partly charged.

• An intelligent charger is that it’s An intelligent charger is that it’s output current depends upon the output current depends upon the battery's state. An intelligent charger battery's state. An intelligent charger may monitor the battery's voltage, may monitor the battery's voltage, temperature and/or time under temperature and/or time under charge to determine the optimum charge to determine the optimum charge current at that instant. charge current at that instant.

• Charging is terminated when a Charging is terminated when a combination of the voltage, combination of the voltage, temperature and/or time indicates temperature and/or time indicates that the battery is fully charged. that the battery is fully charged.

This is the End ofThis is the End of the Reading materials the Reading materials

ExercisesExercises

• Ready to go?Ready to go?

1. Put the Phrases into 1. Put the Phrases into EnglishEnglish

• 11 ）一个理想电压源）一个理想电压源• 22 ）比例常数）比例常数• 33 ）欧姆定律）欧姆定律• 44 ）电子器件）电子器件• 55 ）可变电容）可变电容

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• 66 ）阻挡直流）阻挡直流• 77 ）感抗）感抗• 88 ）电磁能）电磁能• 99 ）交流电频率）交流电频率• 1010 ）输入阻抗）输入阻抗

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2. Put the Phrases into 2. Put the Phrases into ChineseChinese

• 11 ）） linear resistor linear resistor

• 22 ）） be be inversely proportional to inversely proportional to • 33 ）） circuit diagramcircuit diagram

• 44 ）） simplified capacitorsimplified capacitor• 55 ）） pass ac current pass ac current

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• 66 ）） capacitive reactance capacitive reactance • 77 ）） as long asas long as• 88 ）） powered iron corepowered iron core• 99 ）） variable inductorsvariable inductors

• 1010 ）） take into account take into account

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3. Sentence Translation3. Sentence Translation

• 11 ）） Suppose that some material is Suppose that some material is connected to the terminals of an connected to the terminals of an ideal voltage source. ideal voltage source.

• 11 ）假设在某一器件的两端加上一个理想电）假设在某一器件的两端加上一个理想电压源。压源。

• 2) 2) Resistors are used as voltage dividers Resistors are used as voltage dividers to reduce voltage for other device. to reduce voltage for other device.

• 22 ）电阻可用于分压，减小其他器件的电压 ）电阻可用于分压，减小其他器件的电压 。。

• 3) 3) There are many different types of capThere are many different types of capacitor but they all work in essentially the acitor but they all work in essentially the same way. same way.

• 33 ）电容的种类很多，但它们的基本工作原）电容的种类很多，但它们的基本工作原理都是一样的。 理都是一样的。

• 4) The magnitude of the net charge Q on 4) The magnitude of the net charge Q on one plate is proportional to the applied one plate is proportional to the applied voltage V.voltage V.

• 44 ）一块极板上聚集电荷的多少取决于所加）一块极板上聚集电荷的多少取决于所加的电压。 的电压。

• 5) Impedance is more complex than 5) Impedance is more complex than resistance because the effects of resistance because the effects of capacitance and inductance vary with the capacitance and inductance vary with the frequency of the current passing through frequency of the current passing through the circuit.the circuit.

• 55 ））阻抗比电阻复杂，因为电容和电感（对阻抗比电阻复杂，因为电容和电感（对电流的阻碍）作用是会随着流过电路的电电流的阻碍）作用是会随着流过电路的电流的频率变化而变化的。流的频率变化而变化的。

44 ．． TranslationTranslation

• Standard-type resistors usually Standard-type resistors usually maintain their value regardless of maintain their value regardless of external conditions, such as voltage, external conditions, such as voltage, temperature, and light. These types temperature, and light. These types of resistors are referred to as linear of resistors are referred to as linear resistors. resistors.

• There are other types of resistors referreThere are other types of resistors referred to as nonlinear, whose resistance varied to as nonlinear, whose resistance varies with temperature (thermistor s with temperature (thermistor 热敏电热敏电阻阻 ),voltage(varistor),voltage(varistor 变阻器变阻器 ) and light.) and light.

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