电子信息类专业英语,http:/www.cmpbook.com,机械工业出版社同名教材配套电子教案,温丹丽 高源 制作,Passage Two Microwave Ovens,1. When was the first microwave oven invented? 2. How does a microwave oven cook food? 3. Why is the inner wall made of metal? 4. Why the turntable is always turning when you heat something in a microwave oven?,机械工业出版社 http:/www.cmpbook.com,Passage Two Microwave Ovens,Words and Expressions popularity n. 普及，流行 oscillate v. 振荡 magnetron n. 磁控管 waveguide n. 波导管 bounce v. 弹回，弹跳 turntables n. 转盘 mull v. 深思 microwave oven 微波炉 water molecule 水分子 frictional heat 摩擦热,Passage Two Microwave Ovens,Text The microwave oven was invented in the late1940s in the US. During World War II，microwave technology was used a lot in radar equipment，so the technology was advanced. After the war，scientists used the knowledge that they had of microwaves to invent the first microwave oven. In fact，the microwave oven was called a “radar oven” at first because of its history. Back then，microwave ovens were so big that only restaurants and other businesses used them.,Passage Two Microwave Ovens,In the1960s，the first home-use microwave oven was made in Japan. In those days，only rich people could afford it，but nowadays，microwave ovens are more affordable for people in many countries. It is easy to heat up yesterdays leftovers with a microwave oven. As people like you start to understand more about how easy and convenient microwave ovens are，their popularity grow. Next，lets look at how microwave ovens have changed over time. Microwave ovens heat up food using electromagnetic waves called microwaves（hence the name）. These microwaves oscillate（go up and down like a wave in the ocean）2，400，005，000（2.4 billion and 5 thoustand）times every second!,Passage Two Microwave Ovens,Most food contains water. When microwaves hit molecules of water， the molecules start vibrating really fast, which makes the water molecules hit each other and rub against each other. Heat caused by rubbing is called “frictional heat” and this is what starts cooking the food (Fig.6-3).,Passage Two Microwave Ovens,Fig.6-3 Water molecules vibrating,Passage Two Microwave Ovens,If you use fire to heat something，it starts to get hot from the outside and it takes some time before the inside gets hot. But because microwave ovens use the power of microwaves，they can start cooking food from the inside right away. Lets take a look inside a microwave oven. Do you see that thing at the top right of the Fig.6-4? That is what is called a magnetron. This device makes the microwaves that heat and cook your food. The microwaves enter the oven area by traveling through a tube called a waveguide.,Passage Two Microwave Ovens,Fig.6-4 Main components of microwave oven,Passage Two Microwave Ovens,The inner wall is made of metal. This is because microwaves will bounce back off the metal wall and hit your food, even if they miss it the first time. The microwave door has a special screen on it that stops microwaves from escaping outside. In the middle of the microwave oven is the turntable. Do you notice that when you heat something in a microwave oven, the turntable is always turning? When the waveguide tube we talked about before injects microwaves into the inside of a microwave oven, there are always some areas that get hit with a lot of waves and some areas that dont. If food was warmed up like that, there would be parts that are hot and some that are cold, so the food wouldnt taste too good.,Passage Two Microwave Ovens,How do you get the microwaves to hit all parts of the food evenly? Scientists mulled over this question for a very long time and realized that moving the food was a lot easier than trying to make the microwaves reach every corner of the oven evenly. Thats why scientists started using turntables to spin the food inside microwave ovens.,Passage Two Microwave Ovens,Exercises I. Decide whether the following statements are true or false accroding to the text. 1. The microwave oven was invented in the late 1940s in the US. 2. The microwave oven has been already very common in family. 3. When you heat something in a microwave oven, the turntable does not turn. 4. The first home-use microwave oven was made in Japan. 5. Microwaves are injected by the waveguide tube.,Passage Two Microwave Ovens,II. Match the items listed in the following two columns. 1. microwave oven a. 导波管 2. turntable b. 磨擦热 3. frictional heat c. 微波 4. waveguide tube d. 微波炉 5. water molecule e. 水分子 6. magnetron f. 冷却扇 7. microwave g. 磁控管 8. cooling fan h. 转盘,Passage Two Microwave Ovens,III. Complete the following sentences according to the text. 1. The food starts to_ when you use fire, but when you use microwave ovens, the food _. 2. During World War II, microwave technology_