题干

小灯泡L和电阻R上分别标有”6V 4.8W“和“0.6A“字样,它们的电流随电压变化规律如下图所示.现将小灯泡L和电阻R连入电路中,若能确保电路中的元件不损坏,则下列说法错误的是(   )

A:L和R并联时干路中的电流最大可达到1.4A

B:L和R并联时电路的总功率最大可达到8.4W

C:L和R串联时电源电压不超过9V

D:L和及R串联时小灯泡的功率最大可达到1.2W

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答案(点此获取答案解析)

A,B,C

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    Quietly sitting there reading, I found myself suddenly listening to the train guard's announcements. Train travelers will surely agree that when the guard makes an announcement, whether it's the recorded message or the guard's message, few people listen to it, because it's often quite dull or hard to understand. This one was different. I noticed that other passengers appeared to be listening, too. Not only that, everyone was smiling!

    Why was so much attention being paid to this message? As best I can recall, the guard said something along these lines, “Good Morning Ladies, Gentlemen and Children, this is the 7:35 a.m. from Penrith to Central and you'll be pleased to know that we are right on time. And what a lovely morning it is in Sydney today. The sun is shining, birds are singing, and all's right with the world. I trust you have a great day wherever you're going. Thanks for catching my train this morning and I hope to see you again soon.”

    Quite a few people (obviously previous strangers) started talking to one another about the guard's excellent message and how good it had made everyone feel. I started thinking about this, and then I found the young guard and said “Were you the guard on the 7:35 a.m. from Penrith?” The guard seemed a bit stunned at first, replying, “Yes, yyyyes.” “Well, I really appreciate your announcement. Thank you for your extremely good message, which gave me and the other passengers such a good start to the day. Please keep doing it.” I said.

    There are two messages for me in what happened that day. Firstly, when people are happy in their work it shows in what they do and say. Secondly, the story attaches much importance to the benefits that accumulate from thanking people for something they've done, particularly when it's not expected. Can you imagine the conversation that guard would have when he got home?