【英语时差8,16】恒温器的工作原理

 Thermometers just tell you the temperature. Thermostats¹ need to do more than that. In addition to reading the air temperature, thermostats also turn your furnace on if the air gets too cool, and turn it off again when the air heats up. How do they do this? At the heart of many household thermostats is a type of thermometer called a bimetallic coil. This is made from two long, thin strips of metal, usually brass³ and steel, that have been joined firmly together, face to face, like a metallic² sandwich. This new strip, brass on one side and steel on the other, is then coiled into a spiral. Remember that most substances expand when they’re heated and contract when they’re cooled. It’s also true that different substances expand and contract at different rates. In a bimetallic coil, the brass expands and contracts a little bit more than the steel does over the same range of temperature. For example, if the temperature rises, the brass side of the strip will lengthen⁴ slightly more than the steel side. This makes the coil tighten⁵ and loosen with changing temperature.

1 thermostats   

n.恒温（调节）器( thermostat的名词复数 )

参考例句：

• This is the basic operating principle of many thermostats. 这是许多恒温箱的基本工作原理。 来自辞典例句
• Thermostats can be used to regulate the temperature of a room. 恒温器可用来调节室内温度。 来自辞典例句

2 metallic   

adj.金属的；金属制的；含金属的；产金属的；像金属的

参考例句：

• A sharp metallic note coming from the outside frightened me.外面传来尖锐铿锵的声音吓了我一跳。
• He picked up a metallic ring last night.昨夜他捡了一个金属戒指。

3 brass   

n.黄铜；黄铜器，铜管乐器

参考例句：

• Many of the workers play in the factory's brass band.许多工人都在工厂铜管乐队中演奏。
• Brass is formed by the fusion of copper and zinc.黄铜是通过铜和锌的熔合而成的。

4 lengthen   

vt.使伸长，延长

参考例句：

• He asked the tailor to lengthen his coat.他请裁缝把他的外衣放长些。
• The teacher told her to lengthen her paper out.老师让她把论文加长。

5 tighten   

v.(使)变紧；(使)绷紧

参考例句：

• Turn the screw to the right to tighten it.向右转动螺钉把它拧紧。
• Some countries tighten monetary policy to avoid inflation.一些国家实行紧缩银根的货币政策，以避免通货膨胀。