某兴趣小组为检测操场上的风力等级,设计了一台简易风速仪,其工作原理如图甲所示。装有挡风板和滑片P的轻质滑块与轻质弹簧套在滑杆
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmi%3EM%3C%2Fmi%3E%3Cmi%3EN%3C%2Fmi%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
上,滑杆上的摩擦力忽略不计,弹簧左端固定,右端与滑块相连。挡风板的挡风面积为0.2米
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmsup%3E%3Cmrow%3E%3C%2Fmrow%3E%3Cmn%3E2%3C%2Fmn%3E%3C%2Fmsup%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
,均匀电阻丝
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmi%3EA%3C%2Fmi%3E%3Cmi%3EB%3C%2Fmi%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
长为30厘米,阻值为15欧,电源电压
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmi%3EU%3C%2Fmi%3E%3C%2Fmath%3E)
恒为9伏,保护电阻
![](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)
为3欧,电压表量程0~3伏。弹簧弹力
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmi%3EF%3C%2Fmi%3E%3C%2Fmath%3E)
与弹簧长度改变量
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmi%3Ex%3C%2Fmi%3E%3C%2Fmath%3E)
的关系如图乙所示。无风时,滑片P在A处,有风时,滑块移动,稳定后读出电压表示数,计算并查阅下表数据可知风速及风级。
风级 | 一级 | 二级 | 三级 | 四级 | 五级 | 六级 |
风速 (米/秒) | 0.3~1.5 | 1.6~3.3 | 3.4~5.4 | 5.5~7.9 | 8.0~10.7 | 10.8~13.8 |
风压 (帕) | 0.055~1.4 | 1.6~6.8 | 7.2~18 | 18.9~39 | 40~72 | 72.9~119 |