题干

如图所示,开关闭合后小灯泡L1两端的电压是3 V, L2的电阻是12Ω,电源电压是9V, 则L1的电阻是多少?

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答案(点此获取答案解析)

L2两端的电压为:U2=9V-3V=6V,
电路中的电流为:I=U2R2=6V

同类题1

阅读下面文言文选段,完成下列小题。

苏武传

    初,武与李陵俱为侍中。武使匈奴明年,陵降,不敢求武。久之,单于使陵至海上,为武置酒设乐。因谓武曰:“单于闻陵与子卿素厚,故使陵来说足下。终不得归汉,空自苦亡①人之地,信义安所见乎②?且陛下春秋③高,法令亡常,大臣亡罪夷灭④者数十家,安危不可知。子卿尚复谁为乎⑤?愿听陵计,勿复有云!”武曰:“武父子亡功德,皆为陛下所成就,位列将,爵通侯,兄弟亲近⑥,常愿肝脑涂地。今得杀身自效,虽蒙斧钺汤镬⑦,诚甘乐之。臣事君,犹子事父也。子为父死,亡所恨,愿无复再言。”陵与武饮数日,复曰:“子卿,宜听陵言。”武曰:“自分已死久矣!王必欲降武,请毕今日之欢,效死于前!”陵见其至诚,喟然叹曰:“嗟呼!义士!陵与卫律⑧之罪上通于天!”因泣下沾衿⑨,与武决⑩去。

    武留匈奴凡十九岁,始以强壮出,及还,须发尽白。

【注释】①亡:通“无”,没有。②信义安所见乎:信义在哪里显现呢?见:通“现”,显现。③春秋:年纪。④夷灭:被杀。⑤子卿尚复谁为乎:你又替谁(守节)呢?⑥亲近:皇帝的侍从。⑦斧钺:古代兵器;汤镬:古代大锅。⑧卫律:人名。与李陵一样,为投降单于的汉将。⑨衿:衣襟。⑩决:通“诀”。

【背景资料】本文段选自班固所著《汉书》中的《苏武传》。苏武作为汉使出使匈奴,被匈奴扣留,达19年之久,始终没有投降。

同类题5

任务型阅读

    Last month some thieves stole a valuable teapot from a museum in Hong Kong. They took the teapot to America, but the American police found it. The museum sent Mr. Chan, a member of the museum staff, to collect the teapot. On the plane back to Hong Kong, he noticed two men. They were watching him closely. "Perhaps they're going to steal the teapot again. I must think of a plan,” he thought.

    Mr Chan's daughter, Amy, met him at Hong Kong Afimor. Mr Chan NS was carrying two boxes. He gave his daughter the pink box and said to her in a low voice, "Take this gift box home with great care." He walked away with the brown one. The two men followed him.

    Amy opened the box at home. She was expecting a pair of sports shoes, but she just found an old teapot. "This is not a very interesting gift," said Amy, a bit disappointed." That's all right. Let's make some tea in it," said her mother. Then they found a note in the teapot. It said, "Dear Amy, __ Love Dad.”

    The two men kidnapped(绑架)Mr. Chan on his way to the museum. They opened his box and found a pair of sports shoes inside."Wheres the teapot?” the two thieves shouted at the top of their voice with red faces." How dare you cheat us? We saw you give your daughter a box at the airport. Come with us! We're going to search your home, one of them said。

    When the thieves entered Mr. Chan's flat, it was dark and quiet. All of a sudden, the door closed and the lights went on. The police were waiting inside.

    Amy and her mother came out of the bedroom with the teapot. "That teapot is very valuable, said Mr. Chan. "A long time ago it belonged to an emperor. He drank tea from it."

    “We were going to drink tea from it, too, "said Amy, laughing.