现利用热敏电阻
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmsub%3E%3Cmi%3ER%3C%2Fmi%3E%3Cmi%3Et%3C%2Fmi%3E%3C%2Fmsub%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
制作温度报警器,它的阻值随温度t变化的部分数据如下表所示,由表格可知,热敏电阻的阻值随环境温度的升高而
(选填“增大”成“减小”);报警器的一部分电路如图所示,图中两个虚线框中,一个为热敏电阻
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmsub%3E%3Cmi%3ER%3C%2Fmi%3E%3Cmi%3Et%3C%2Fmi%3E%3C%2Fmsub%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
, 一个为定值电阻
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmsub%3E%3Cmi%3ER%3C%2Fmi%3E%3Cmn%3E0%3C%2Fmn%3E%3C%2Fmsub%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
, 电源电压恒为12V。 当环境温度升高,电压表示数达到或超过8V时,便触发报警器(图中未画出)报警,则热敏电阻应接在虚线框
(选填数字“1”或“2”)内。 不考虑报警器对电的影响,要求环境温度达到或超过60℃时开始报警,则
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmsub%3E%3Cmi%3ER%3C%2Fmi%3E%3Cmn%3E0%3C%2Fmn%3E%3C%2Fmsub%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
的阻值为
Ω。
环境温度t/℃ | 5 | 10 | 20 | 30 | 40 | 50 | 60 |
热敏电阻![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmsub%3E%3Cmi%3ER%3C%2Fmi%3E%3Cmi%3Et%3C%2Fmi%3E%3C%2Fmsub%3E%3Cmtext%3E%2F%CE%A9%3C%2Fmtext%3E%3C%2Fmrow%3E%3C%2Fmath%3E) | 6000 | 4400 | 2800 | 1800 | 1100 | 800 | 700 |
![](http://tikupic.21cnjy.com/2023/02/20/9d/2d/9d2dc5b2624df6e8ac0076b55a827deb_178x180.png)