中職電子專業(yè)英語第4章教學課件

1、正版可修改PPT課件(中職）電子專業(yè)英語第4章教學課件Warming-upI. Can you point out what kind of resistor components they are in the following pictures?II.Do you know what the following abbreviations or symbols stand for?LDRLEDLCRIII.Talk about Current in English. And the following patterns you can use: Do you know the symbo

2、l R?Could you tell me how many kinds of resistors there are? And what are they?Unit 4 Resistance下一頁返回Could you tell me the unit of resistance?What is the symbol of resistance?The unit / symbol of resistance is Text Comprehension ResistanceIn electricity, resistance is the opposition to current flow

3、in a body when there is a potential difference between the ends of the body. In order to compare the resistance of different substances, it is necessary to consider the resistance offered by a sample of fixed dimensions. It is usual to choose a cube as the sample body, and the dimensions of the cube

4、 will depend on the system of units we employ. The resistance between opposite face of this sample cube is called resistivity, which is the electric field per unit current density. The greater the resistivity, the greater the field needed to establish a given current density, or the smaller the curr

5、ent density caused by a given field. Unit 4 Resistance上一頁下一頁返回A “perfect” conductor would have zero resistivity, and a “perfect” insulator would have infinite resistivity. Metals and alloys having the lowest resistivities are the best conductors.Experiments show that the resistance of a wire is dire

6、ctly proportional to its length, inversely proportional to its crosssectional area, and directly proportional to the resistivity of the substance forming the wire. Resistance components are as follows: heating elements, resistors, variable resistors, thermistors and lightdependent resistors(LDRs). I

7、f the resistors are connected in seriesThe greater the resistance, the larger the opposition to current, the more the potential drop. Therefore, the resistors can be used to control the current and voltage in the circuit, thats to say, to decrease voltage, divide voltage or current, and restrict the

8、 current, and so on.The resistors have values measured in ohms. A resistor of 100is a much greater obstacle of current than a resistor of 10. variable resistors have values that can be altered so it is possible to adjust the current flow in a circuit.Unit 4 Resistance上一頁下一頁返回Vocabulary1. opposition

9、n. 相對，對抗 9. establish v. 建立，形成2. compare v. 比較，對照 10. variable adj.可變的，可調的3. substance n. 物質 11. resistor n. 電阻器4. sample n. 樣品，標本 12. thermistor n. 熱敏電阻5. dimension n. 尺寸，量綱 13. restrict v. 限制，節(jié)流6. cube n. 立方體 14. obstacle n. 障礙，阻礙7. density n. 密度，強度 15. alter v. 改變，變更8. resistivity n. 電阻率 16. adju

10、st v. 調節(jié)，調整Phrases and expressions1.depend on依賴，取決于2.cross-sectional area橫截面積3.heating elements發(fā)熱元件Unit 4 Resistance上一頁下一頁返回4.lightdependent resistors光敏電阻5.connect in series串聯(lián)6.as follows如下Notes1. A “perfect” conductor would have zero resistivity. 譯成：理想的導體具有零電阻率?；蛘撸豪硐氲膶w電阻率為零。此處 “perfect”譯成“理想的”而不要譯

11、成“完美的”。2. “having the lowest resistivities”該短語是現(xiàn)在分詞短語作后置定語。3. “the resistors can be used to control the current and voltage in the circuit”全句譯為 “ 電阻器可用來控制電路中的電流和電壓，即可用來降壓、分壓、分流、限流等等?！盪nit 4 Resistance上一頁下一頁返回I Choose the right answer from A, B, and C according to the text. 【 】1.The unit of the resis

12、tance is _.A. voltB. ampereC. ohm【 】2. The current density depends on _.A. resistanceB. resistivityC. current【 】3. A conductor has _ resistivity than an insulator.A. greaterB. smallerC. Not mentioned.【 】4. The resistance of a wire is related to its _.A. lengthB. cross-sectional areaC. both A and B【

13、】5. The value of _ can be altered to adjust the current in a circuit.A thermistorsB. variable resistorsC. LDRUnit 4 Resistance上一頁下一頁返回II True or false.1. The resistance is opposite to the current in a circuit.2. The smaller the resistivity, the smaller the current density caused by a given field.3.

14、The resistance of a wire is inversely proportional to the resistivity of the substance forming the wire.4. The resistors can be used to divide voltage or current. 5. The resistors have values in the unit of ohm.III Translate the following sentences.1. In electricity, resistance is the opposition to

15、current flow in a body when there is a potential difference between the ends of the body.2. The greater the resistivity, the greater the field needed to establish a given current density.Unit 4 Resistance上一頁下一頁返回3. Experiments show that the resistance of a wire is directly proportional to its length, inversely proportional to its crosssectional area, and directly proportional to the resistivity of the substance forming the wire.4. The greater the resistance, the larger the opposition to current, the more the potential drop.5. the resistors can be us