某同学将一直流电源的总功率PE、输出功率PR和电源内部的发热功率_爱下问搜题

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问题选择题

某同学将一直流电源的总功率P_E、输出功率P_R和电源内部的发热功率P_r随电流I变化的图线画在了同一坐标上，如右图中的a、b、c所示，下面说法正确的是

A．反映P_r变化的图线是c

B．电源电动势为8V

C．电源内阻为2Ω

D．当电流为0.5A时，外电路的电阻为6Ω

答案

ACD

电源的总功率P_E=EI，p-I图像是一条直线，所以a表示P_E，A正确；电源内部的发热功率P_r=I²r, p-I图像是一条开口向上的抛物线，所以c表示P_r，b表示输出功率P_R。由图像可知当I=2A时，P_E=8W，所以电动势E=P_E/I=4V，B错误；由图像可知当I=2A时，P_r=8W，所以内阻r= P_r/I²=2Ω，C正确；当电流为0.5A时，有闭合电路的欧姆定律有：，解得，D正确。

单项选择题

休梅克线正常时应：

A．两连线相交于脐

B．两连线相交于脐下

C．两连线偏离中线

D．两连线平行

E．两连线垂直

完形填空

I still remember father spent plenty of time teaching me how to pronounce a word, how to understand something that I saw for the first time and how to be polite to others. And I will never 31   one sentence my father used to say to me, “I love you, son. Say you love me, son.” 32  , I would scream, “I love you, Dad.”
When I was growing up, I found that I had little in 33 with my father gradually. Sometimes we often argued about something sharply and then the argument changed into a 34 . I knew there was a gap between us. I didn’t 35 hearing the words “I love you” from my father the last time. To tell you the truth, I couldn’t honestly remember 36 I had last said those words to him, either.
Now father was in hospital. The doctor said it was 37 and he needed an operation at once, 38   he wasn’t sure whether my father was able to 39 it. Everything in my childhood 40 in my mind. Then I called and said, “Dad, I love you!”
There was a   41   at the other end and he replied coldly, “Well, I love you, too!”
I   42   and said, “Dad, I know you love me, and when you are   43 , I know you will say what you want to say.”
Fifteen minutes later my mother called and 44  asked, “Paul, is everything OK?”
A few weeks later I was working when I received my father’s call. “Paul, I love you.” I was so 45 that my tears rolled down my cheeks. Perhaps both of us 46 that this special moment had 47 our relationship to a new level.
A short while after this special moment, my father finally narrowly   48 death following the heart operation. I can’t 49 that if I didn’t take the first   50 and Dad did not survive the surgery, what kind of life I would lead now.