Project 2 Current, Voltage and Resistance

Task 1 Question Import

1.What is the current and its unit?

2.What is the voltage and its unit?

3.What is the resistance and its unit?

4.What is the “Ohm's Law”?

Task 2 Reading and Understanding

The flow of electrons through a conductor is called a current.Current flow is represented by the letter symbol I.The basic unit in which current is measured is the ampere (A).One ampere of current is defined as the movement of one coulomb (6.28×1018electrons) past any point of a conductor during one second of time.

When it is desirable to express a magnitude of current smaller than the ampere, the milliampere (mA) and the microampere (μA) units are used.One milliampere is equivalent to one-thousandth (0.001) of an ampere, and one microampere is equivalent to one-millionth (0.000001) of an ampere.

The term voltage (represented by the letter symbol U or V) is commonly used to indicate both a difference in potential and an electromotive force.The unit in which voltage is measured is the volt.One volt is defined as that magnitude of electromotive force required cause a current of one ampere to pass through a conductor having a resistance of one ohm.

A magnitude of voltage less than one volt is expressed in terms of millivolts (mV) or microvolts (μV).Larger magnitudes of voltage are expressed in kilovolts (kV).One kilovolt equals one thousand volts.

The opposition to current is called electrical resistance and is represented by the letter symbol R.The unit of resistance is the ohm, a term that is often expressed by using Ω.One ohm is defined as that amount of resistance that will limit the current in a conductor is one ampere when the voltage applied to the conductor is one volt.Larger amounts of resistance are commonly expressed in kiloohm (kΩ) and in megohm (MΩ).

The relationship between volts, amperes, and ohms can be represented by “Ohm's Law”.“Ohm's Law” states that the ratio of the voltage between the ends of a wire and the current flowing in it is equal to the resistance of the wire.Now we can say that when a given voltage is applied across the ends of the wire, an electric current always flows along it, and the value of this current depends on the resistance of wire (as shown in Fig.2-1).

New Words

measure['meʒə]v.&n.　　　　　　　测量；方法，尺度

ampere['æmpɛə]n.　　　　　　　　 安培

coulomb['ku:lɔm]n.　　　　　　　　库仑

magnitude['mægnitju:d]n.　　　　　　大小，数量，巨大，广大

equivalent[i'kwivələnt]adj.　　　　　 相等的，相同的，等量的

volt[vəult]n.　　　　　　　　　　 伏特

Phrases and Expressions

less than　　　　　　　　　　　　 毫不，完全不，一点都不

electromotive force　　　　　　　　 电动势

Notes

1.The flow of electrons through a conductor is called a current.

译文：通过导体的电子流称为电流。

2.The basic unit in which current is measured is the ampere (A).

译文：度量电流的基本单位是安培（A）。

句中in which current is measured是定语从句，修饰unit。

3.be defined as

“给……下定义为”，后可接名词或宾语从句，如课文中第一段最后一句。

4.When it is desirable to express a magnitude of current smaller than the ampere, the milliampere (mA) and the microampere (μA) units are used.

译文：当需要表示比安培小的电流量时，可用毫安（mA）和微安（μA）。

it是形式主语，不定式to express a magnitude of current smaller than the ampere充当真正的主语。

5.One volt is defined as that magnitude of electromotive force required cause a current of one ampere to pass through a conductor having a resistance of one ohm.

译文：使1安培电流通过电阻为1欧姆的导体所需的电动势定义为1伏特。

（1）过去分词required，充当后置定语，修饰electromotive force。（2）having a resistance of one ohm 是现在分词短语，充当后置定语，修饰conductor。

6.The unit of resistance is the ohm, a term that is often expressed by using Ω.

译文：电阻的单位是欧姆，常用Ω表示。

a term…为ohm的同位语，其中that is often expressed by using Ω是定语从句，修饰term。

7.One ohm is defined as that amount of resistance that will limit the current in a conductor is one ampere when the voltage applied to the conductor is one volt.

译文：1欧姆的定义是，当加到导体上的电压为1伏特时，将导体中的电流限制为1安培所需的电阻值。

that引导定语从句，修饰amount of resistance，其中when the voltage applied to the conductor is one volt是时间状语从句。

8.The relationship between volts, amperes, and ohms can be represented by “Ohm's Law”.

译文：伏特、安培和欧姆之间的关系可用欧姆定律表示。

欧姆定律，即电阻等于电压除以电流，R = V/I。

Task 3 Read aloud: Prepare for Task 1

1.The current is the flow of electrons through a conductor.The unit of current is ampere.

2.The voltage is difference in potential and electromotive force.The unit of voltage is volt.

3.Resistance is the opposition to current.The unit of resistance is ohm.

4.“Ohm's Law” express the relationship between volt, ampere and ohm.

Task 4 Reading Ability Training

1.Write T (True) or F (False) beside the following statements about the text.

a.Current flow is represented by the letter symbol I.

b.One milliampere is equivalent to one-thousandth (0.001) of an ampere, and one microampere is equivalent to one-billionth (0.000000001) of an ampere.

c.The term voltage is commonly used to indicate a difference in potential but electromotive force is not.

d.One kilovolt equals one thousand volts.

e.The opposition to current is called electrical resistance.

f.Larger amounts of resistance are commonly expressed in kiloohm (kΩ) and in megohm (MΩ).

g.The flow of electrons through a conductor is called a resistance.

h.One volt is defined as that magnitude of electromotive force required cause a current of one ampere to pass through a conductor having a resistance of one ohm.

2.Match the following terms to appropriate definition or expression.

a.current　　　　　　1.electromotive force

b.amp　　　　　　　2.the relationship between volts,amperes,and ohms

c.voltage　　　　　　3.the flow of electrons

d.ohm　　　　　　　4.the unit of resistance

e.Ohm's Law　　　　 5.the unit in which current is measured

3.Fill in the missing words according to the text.

a.One ampere of current is defined as the movement of______coulomb (6.28×1018electrons) past any point of a conductor during______second of time.

b.One milliampere is equivalent to __________(0.001) of an ampere, and one microampere is equivalent to______(0.000001) of an ampere.

c.One volt is defined as that magnitude of electromotive force required cause a current of one______to pass through a conductor having a__________of one ohm.

d.One ohm is defined as that amount of______that will limit the current in a conductor is one ampere when the______applied to the conductor is one volt.

4.Translate the following paragraphs into Chinese.

Potential

The unit for potential difference, or electromotive force, is the volt.The abbreviation, or symbol, for this unit is V.Voltage is expressed in volts.Recall that one volt equals the amount of electromotive force (emf) that moves a current of one ampere through a resistance of one ohm.

Current

The unit of measure for current flow is the ampere.The abbreviation, or symbol, for this basic unit of measure is A.Remember that one ampere equals an electron flow of one coulomb per second past a given point.

Resistance

Resistance is another electrical parameter that two letter: “R” represents the general term resistance and the Greek letter omega (Ω) represents the unit of resistance, the ohm.Remember that one ohm equals the resistance that limits the current to one ampere with one volt applied.

Conductance

Another electrical parameter is conductance.Conductance is the opposite of resistance.The unit of conductance is the siemens (S) named after the scientist Ernst Siemens.The abbreviation for the general term conductance is G.

5.Translate the following sentences into English.

a． 电压的单位是伏特，用符号V表示。

b． 电流的单位是安培，用符号A表示。

c.1伏特的电压施加在导体上产生了1安培的电流，此时电阻为1欧姆。

d． 欧姆定律表示了安培、伏特、欧姆之间的关系。

Chinese Translation of Texts（参考译文）

项目2 电流、电压和电阻

通过导体的电子流称为电流。电流用字母符号I表示。度量电流的基本单位是安培（A）。1安培电流的定义是，在1秒钟内有1库仑（6.28×1018个电子）的电量通过导体的任何一点时的电流为1安培。

当需要表示比安培小的电流量时，可用毫安（mA）和微安（μA）。1毫安等于0.001安培， 1微安等于0.000001安培。

电压这个术语（用字母符号V表示）常用来表示电位差和电动势。度量电压的单位是伏特。使1安培电流流过电阻为1欧姆的导体所需的电动势定义为1伏特。

小于1 V的电压值用毫伏（mV）或微伏（μV）表示。较高的电压值可用千伏（kV）表示。1 kV等于1000 V。

电流的阻力叫作电阻，用字母符号R表示。电阻的单位是欧姆，常用Ω表示。1欧姆的定义是，当加到导体上的电压为1伏特时，将导体中的电流限制为1安培所需的电阻值。较大的电阻值常用千欧（kΩ）和兆欧（MΩ）表示。

伏特、安培和欧姆之间的关系可用欧姆定律表示。欧姆定律描述为导线两端电压与流过导线的电流的比是导线的电阻。可以认为当在导线两端施加一个给定电压时，导线中总是有电流，电流的值取决于导线的电阻（如图2-1所示）。