microwave oven.ppt

1、English for Electronic Technology,Passage Four Microwave Oven,Unite Two Electronic Products,Key points: useful terms and the working principles of microwave oven Difficult points: describing the structures and working processes of a microwave oven,Leading in-Revision,Talk about refrigerators Main co

2、mponents of a refrigerator Function of each component,Leading in-Revision (watch and listen),TV in Refrigerator How air conditioning work? Talk about refrigerator,Microwave Oven,microwave maikruweiv n. 微波 oven vn n. 烤炉,烤箱,When was microwave oven invented?,The microwave oven was invented by American

3、electrical engineer Percy Spencer (1894-1970 ) in 1946. Dr. Spencer held 150 patents and was considered one of the worlds leading experts in the field of microwave energy.,The first microwave was about 5 feet high, 750 pounds and selling for $5,000 each.,Who was the inventor?,How were microwave oven

4、s invented?,1946 during a radar-related research project Dr. Percy Spencer noticed something very unusual. He was testing a new vacuum tube called a magnetron when he discovered that the chocolate bar in his pocket had melted. Later he held a package of popcorn near a magnetron, popcorn exploded all

5、 over the lab. Spencer had discovered that you could cook with electromagnetic waves.,magnetron mgnitrn n. 磁电管 -tron是后缀，表示“真空管、电子管,A Paragraph from Text,The microwave oven was invented in the late 1940s in the US. During World War II, microwave technology was used a lot in radar equipment, so the te

6、chnology 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 u

7、sed them.,About the first home-use microwave oven,In the 1960s, 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.,构词法-合成法（compounding）由两个或两个以上的词合成一个新词，或连字符连接，或直接连接在一起。,

8、home-use leftover waveguide turntable hardware firmware,家用 残留物,剩饭 n. 波导管n. 转车,转盘五金器具n. (计算机) 硬件 n. 固件,About the first home-use microwave oven,From internet The first microwave oven designed for home use was a 24-inch oven, produced by the Tappan Stove Company around 1955. At $1295, they were conside

9、red a luxury and sales were moderate. Now Microwave Ovens Sell For As Low As $50,moderate mdrit neither small nor large but between the two,How does microwave cook food?,Microwave ovens heat up food using electromagnetic waves called microwaves (hence the name!). These microwaves oscillate (go up an

10、d down like a wave in the ocean) 2,400,005,000 (2.4 billion) times every second!,oscillate sileit v. 振动 -local crystal oscillator本地晶体振荡器 vibrate -vibrator,What is frictional heat?,Most food contains water. When microwaves hit molecules of water, the molecules start vibrating really fast, which makes

11、 the water molecules hit each other and rub against each other.,A a,Heat caused by rubbing is called frictional heat and this is what starts cooking the food. Now you understand how microwave ovens cook food,molecule mlikju:l n. 分子 Alcohol molecule is composed of the carbon, hydrogen and oxygen elem

12、ents. friction frikn n. 摩擦,摩擦力adj:frictional,How does microwave cook food?,If you use fire to heat something, you know that 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 fr

13、om the inside right away.,Structures of a microwave oven,Do you see that thing at the top right of the picture? That is what is called a magnetron. The microwaves that heat and cook your food are made by this device! The microwaves enter the oven area by traveling through a tube called a waveguide.,

14、Magnetron,The heart of a microwave oven is the magnetron. A magnetron converts electrical energy to microwave radiation. To do this, it uses low-voltage alternating current and high-voltage direct current. A transformer changes the incoming voltage to the required levels and a capacitor, in combinat

15、ion with a diode, filters out the high voltage and converts it to direct current.,Whats the inner wall of a microwave oven made of? why?,The inner wall is made of metal. This is because microwaves will bounce back off the metal wall and hit your food, even if it misses it the first time. The microwa

16、ve door has a special screen on it that stops microwaves from escaping outside.,The function of the turntable,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.

17、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.,The function of the turntable,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