中職電子專(zhuān)業(yè)英語(yǔ)第3章教學(xué)課件

1、正版可修改PPT課件(中職）電子專(zhuān)業(yè)英語(yǔ)第3章教學(xué)課件Warming-up I.Can you point out the difference of the following pictures?II.Do you know what the following formulas stand for?(1) UB = WB /q UA = WA /q (2) UBA = (WB -WA ) /q(3) Unit 3 EMF下一頁(yè)返回III.Talk about Current in English. And the following patterns you can use: Do you

2、 know how electricity flows?Could you tell me how many kinds of current / voltage there are? And what are they?Could you tell me the unit of current / voltage?What is the symbol of current / voltage?The unit / symbol of current / voltage is Text Comprehension EMFIn order for a steady current to exis

3、t in a conducting path there must be a closed loop. Otherwise charge would accumulate at the ends of the conductor, the resulting electric field would change with time, and the current could not be constant.Unit 3 EMF上一頁(yè)下一頁(yè)返回However, such a path cannot consist entirely of resistance. Current in a re

4、sistor requires an electric field and an associated potential difference. The field always does positive work on the charge, which always moves in the direction of decreasing potential. But after a complete trip around the loop, the charge returns to its starting point, and the potential there must

5、be same as when it left that point. This is impossible if the trip around the loop involves only decreases in potential.Thus in a circuit, there must be some part of the loop where a charge travels from lower to higher potential, despite the fact that the electrostatic force is trying to push it fro

6、m higher to lower potential. This driving force to tend to produce the flow of charges through a circuit is called an electromagnetic force (or EMF). It is measured in volts. The EMF makes charges flow from one point in the circuit to another. The greater the EMF, the greater the pressure on the cha

7、rges. A battery is a device to produce a potential difference necessary to cause electrons to flow along a conductor.Unit 3 EMF上一頁(yè)下一頁(yè)返回It is necessary to distinguish between an EMF and a potential difference. A battery is a source of EMF, whereas the voltage across a resistance is a potential differ

8、ence. If an EMF is applied to a path to allow the charges to pass, they will move toward the point of higher potential and then a current is said to exist in the circuit.Vocabular 1. steady adj. 穩(wěn)定的，固定的2. conduct v. 傳導(dǎo)，引導(dǎo)3. accumulate v. 堆積，聚集4. entirely adv. 完全地，徹底地 5. resistance n. 電阻6. constant n

9、. 常數(shù)； adj. 恒定的，不變的7. associate v. 聯(lián)合，結(jié)合8. decrease v. 減少，降低9. electrostatic adj. 靜態(tài)的Unit 3 EMF上一頁(yè)下一頁(yè)返回10. electromagnetic adj. 電磁的11. force n. 力量，勢(shì)，強(qiáng)度12. distinguish v. 區(qū)別，辨別Phrases and expressions1.closed loop閉合回路2.potential difference電勢(shì)差，電位差3.EMF電動(dòng)勢(shì)4.electrostatic force 靜電力Notes1. “in order for a

10、steady current to exist in a conducting path” means “for a steady current, in order to exist in a conducting path, ”2. “The field always does positive work on the charge”. Here “work” means “功”, “does work” means “做功”，此處“positive”意思是“正的”Unit 3 EMF上一頁(yè)下一頁(yè)返回3. “to tend to produce the flow of charges th

11、rough a circuit”不定式作定語(yǔ)，修飾“the driving force”?！皌o produce a potential difference necessary to cause electrons to flow along a conductor”也是不定式作定語(yǔ)，修飾“a device”?！皌o distinguish between an EMF and a potential difference”此處不定式用作真正的主語(yǔ)，“it”是形式主語(yǔ)。I Choose the right answer from A, B, and C according to the te

12、xt. 【 】1.A current is the flow of _.A. chargesB. positive chargesC. electrons【 】2. The current flows in a _.A. closed circuitB. open circuitC. any circuit【 】3. We use _ in the telephone.A. ACB. DCC. Not mentioned.【 】4. _ flows first in one direction and then in another.A. AC B. DC C. Not mentioned.U

13、nit 3 EMF上一頁(yè)下一頁(yè)返回【 】5. _ can change the alternating current into direct current.A TransformerB ReceiverC RectifierII True or false.1. The electrons moves from plus to minus.2. The current flows from the positive to the negative terminal.3. The direct current can easily increase and decrease its volt

14、age.4. The transformer can transform a low voltage into a high voltage and vice versa. 5. The rectifier is used to change a direct current into an alternating current.III Translate the following sentences.1. The electrons flow along a wire much the same way as water runs through a pipe.2. The electr

15、ic current is conventionally considered to flow from the positive to the negative terminal in a completed circuit.Unit 3 EMF上一頁(yè)下一頁(yè)返回3. The current which moves continuously in one direction is called a direct current.4. At present, practically most cities make use of another type of electric current for lighting, heating, industry and other purpose.5.