题干

有一交变电流如图所示,则由此图象可知(  )

A:它的峰值是4 A

B:它的周期是1.0 s

C:它的有效值是2 2  A

D:每一个周期内电流方向改变一次

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答案(点此获取答案解析)

A

同类题1

课外阅读

       蒙蒙的小雨正落着,陈红骑着自行车悠然于柏油路上。她没有穿雨衣,因为她觉得在这样细雨中骑车很浪漫。她望着路两边来去匆匆的行人,心想:这些人真是的,干嘛要东躲西藏的。忽然_____迎面一辆_____的士_____飞驰而来_____她猛地拐向路边_____但车把挂在树干上_____她摔倒了_____小妹妹_____没事吧 _____一个小伙子站在她身边问道_____陈红白了他一眼,没有理他。心想:谁是你的小妹妹?她一翻身想站起来,可左腿的剧痛却使她不得不重新坐在地上,她接连两次试图站起来,都没成功。最后,只好放弃了努力。小伙子一笑,“别逞强了,还是送你上医院吧。”接着,拉起陈红的车子,又扶陈红坐到车架上,推起车子向医院走去。温柔如丝的春雨淅淅沥沥地落着。陈红已不再潇洒,只感到沉重。她坐在车上,望着前面推车的小伙子,不知该说些什么。她发现小伙子走路不太自然,仔细观察,只见小伙子左腿的袜端与裤腿之间不时地露出一段刺目的棕色。那是什么?啊,他装着一只假腿。陈红想问问他的腿,却却不愿张嘴。这时,只听到小伙子自言自语地说:“三年前,我也喜欢在细雨中骑车,那的确很潇洒,可是我却重重地跌倒了,像你一样。不,还不如你。”“噢,你的左腿——?”停了一会儿,小伙子说:“就在那次跌倒时被后面的汽车轧断了。”听了这话,陈红陷入了沉思。

        医院到了,小伙子搀着陈红进了急诊室。“我去通知你父母,你知道他们的电话吗?”陈红把号码告诉了他。不一会儿,陈红的父母风风火火地赶来了。见到女儿腿上雪白的绷带,忙问这问那。陈红把经过告诉了他们,又说,“要不是那位大哥哥,我真不知该怎么办好,哎,他呢?”这时,只听护土小姐说:“那个小伙子,看见你爸妈来后,他就离开医院了。”陈红怔住了:“我还不知他叫什么呢!”

       父亲背起陈红,母亲在旁边扶着,一家人走出医院的时候,他们多么希望在人流中再次寻到那小伙子的身影。

同类题2

阅读理解

    People in the western state of California who are in the United States illegally can now request a driver's license. The law went into effect on January l. California is not the first American state with such a law, but it has the largest number of illegal immigrants. More than a million people began to request licenses shortly after the new state law went into effect. Among them was Christian Alvarado. Mr. Alvarado entered the United States from El Salvador eight years ago without permission from the U.S. government. Some call such people "illegal immigrants." Others call them "undocumented immigrants".

    Mr. Alvarado thinks it so exciting, for he has been waiting for the license for a long time. But some are worried that their personal information will be used to find them and deport them. Armando Botello is a spokesman for the California Department of Motor Vehicles, or DMV. He says people should not be afraid, for such information will not be shared.

    The new licenses are the same as licenses given to citizens except that they have the words "Federal Limits Apply". That means the license cannot be used to travel on an airplane or enter a federal building. Ana Garcia, working at the Central American Resource Center, says some illegal immigrants fear those words will be used to abuse them. Civil rights groups say the police and others will not.

    Dan Schnur, a political scientist at the University of Southern California, said that the main argument against the new law is that it rewards illegal behavior. But Professor Schnur argued that young, white Americans generally support immigration reform, including giving driver's licenses to illegal immigrants

    "It's simply because they grew up in a much more multicultural society than their parents or their grandparents did." Professor Schnur says he believes the changes in beliefs about illegal immigrants that have taken place in California will spread throughout the United States.