题目内容
频率为50 Hz的交变电流,其电压u=120
sinωt V,把它加在激发电压、熄灭电压均为84 V的霓虹灯的两端,则在半个周期内霓虹灯点亮的时间为______________.(
=1.4)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114035719225.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114035719225.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114035735290.gif)
T=
s="0.02" s,Um=120
V="168" V.
画出U-t图如下图.因为U>84 V时霓虹灯才发光,由图知半个周期灯管点亮的时间Δt=t2-t1,由u=168sin(2πft) V="8" V可知:当2πft=
时,t1=
s,当2πft=
π时,t2=
s.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241140361092491.jpg)
所以Δt=t2-t1=
s=
×
s.
即霓虹灯在半个周期内,有23的时间被点亮,Δt=
s.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114035750263.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114035719225.gif)
画出U-t图如下图.因为U>84 V时霓虹灯才发光,由图知半个周期灯管点亮的时间Δt=t2-t1,由u=168sin(2πft) V="8" V可知:当2πft=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114035984240.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114036016305.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114036031235.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114036078307.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241140361092491.jpg)
所以Δt=t2-t1=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114035735290.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114036125224.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114036203291.gif)
即霓虹灯在半个周期内,有23的时间被点亮,Δt=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114035735290.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
练习册系列答案
相关题目