一只氖管的起輝電壓與交變電流u=50sin314t(V)的有效值相等,若將此交變電流接到氖管的兩極,在一個(gè)周期內(nèi),氖管的發(fā)光時(shí)間為( )
A.0.02s
B.0.015s
C.0.01s
D.0.005s
【答案】
分析:氖管的起輝電壓為25
![](http://thumb.zyjl.cn/pic6/res/gzwl/web/STSource/20131029192609974006006/SYS201310291926099740060003_DA/0.png)
V,由表達(dá)式求出所對應(yīng)的時(shí)刻,再求比25
![](http://thumb.zyjl.cn/pic6/res/gzwl/web/STSource/20131029192609974006006/SYS201310291926099740060003_DA/1.png)
V大的時(shí)間段.
解答:解:根據(jù)交流電的瞬時(shí)表達(dá)式知:當(dāng)瞬時(shí)值為U=25
![](http://thumb.zyjl.cn/pic6/res/gzwl/web/STSource/20131029192609974006006/SYS201310291926099740060003_DA/2.png)
V時(shí),對應(yīng)于四個(gè)時(shí)刻(一個(gè)周期內(nèi)),
即:25
![](http://thumb.zyjl.cn/pic6/res/gzwl/web/STSource/20131029192609974006006/SYS201310291926099740060003_DA/3.png)
=50sin314t V,
sin314t=
![](http://thumb.zyjl.cn/pic6/res/gzwl/web/STSource/20131029192609974006006/SYS201310291926099740060003_DA/4.png)
,
所以t
1=
![](http://thumb.zyjl.cn/pic6/res/gzwl/web/STSource/20131029192609974006006/SYS201310291926099740060003_DA/5.png)
s、t
2=
![](http://thumb.zyjl.cn/pic6/res/gzwl/web/STSource/20131029192609974006006/SYS201310291926099740060003_DA/6.png)
s、t
3=
![](http://thumb.zyjl.cn/pic6/res/gzwl/web/STSource/20131029192609974006006/SYS201310291926099740060003_DA/7.png)
s、t
4=
![](http://thumb.zyjl.cn/pic6/res/gzwl/web/STSource/20131029192609974006006/SYS201310291926099740060003_DA/8.png)
s,
所以
![](http://thumb.zyjl.cn/pic6/res/gzwl/web/STSource/20131029192609974006006/SYS201310291926099740060003_DA/9.png)
=0.01s,故C正確;
故選C
點(diǎn)評:在交流電的一個(gè)周期內(nèi),瞬時(shí)值相等的點(diǎn)有四個(gè),最好畫出圖象分析.