问题 选择题

如图为小科设计的遮光感烟探测器部分工作原理图,在一个外部光线无法进入的烟室中,装有一个激光发生器及带有感光电阻(R0)的电路,R为定值电阻,电源电压恒定;当烟雾进入烟室后,激光被烟雾遮挡而使感光电阻的阻值发生变化.当烟雾达到某一浓度时,探测器便会发出警报.已知光照越强,感光电阻阻值越小,反之则越大.当烟室中烟雾越来越浓时,则(   )

A.电路的总电阻逐渐变小

B.电压表的示数逐渐变大

C.电流表的示数逐渐变大

D.定值电阻R消耗的功率逐渐变大

答案

答案:B

题目分析:由图知感光电阻(R0)与R串联,电流表测量的是通过电路中的电流,电压表测量的是R0两端的电压。由题意知:当烟室中烟雾越来越浓时,光照越弱,感光电阻阻值越大,A选项中电路的总电阻变大;B、C选项中电源电压恒定时,通过电路中的电流变小;定值电阻R两端电压变小,R0两端电压变大;D选项由P=I2R知,电流变小,R不变,故P变小;所以本题选项是B。

阅读理解

阅读理解。

      Horror gripped (紧握) the heart of the World War I soldier as he saw his lifelong friend fall in battle.

Caught in a trench with continuous gunfire whizzing (子弹等在空中掠过的声音) over his head, the soldier

asked his lieutenant (陆军中尉), if he might go out into the"No Man's Land"between the trenches to bring

his fallen comrade back.

     "You can go," said the lieutenant, "but I don't think it will be worth it. Your friend is probably dead and

you may throw your own life away."The lieutenant's words didn't matter, and the soldier went anyway.

     Miraculously he managed to reach his friend, hoisted (扯起) him onto his shoulder, and brought him

back to their company's trench. As the two of them tumbled in together to the bottom of the trench, the

officer checked the wounded soldier, then looked kindly at his friend. "I told you it wouldn't be worth it, "

he said. "Your friend is dead, and you are mortally wounded."

     "It was worth it, though, sir," the soldier said.

     "How do you mean'worth it?'"responded the lieutenant. "Your friend is dead!"

     "Yes sir," the private answered."But it was worth it because when I got to him, he was still alive, and I

had the satisfaction of hearing him say,'Jim, I knew you'd come.'"

     Many a time in life, whether a thing is worth doing or not really depends on how you look at it. Take up

all your courage and do something your heart tells you to do so that you may not regret not doing it later in

life.

1. What's the lieutenant's attitude towards the soldier's saving his friend?

A. Negative.

B. Positive.

C. Neutral.

D. Supportive.

2. The underlined word "Miraculously" can be replaced by _____.

A. Happily

B. Excitedly

C. Surprisingly

D. Disappointedly

3. According to the soldier, why did he say "It was worth it."?

A. Because the soldier saved his friend in time.

B. Because the soldier successfully brought his friend back.

C. Because what he did will bring him great honor and make him get promoted in his later life.

D. Because his friend was still alive when he reached him and he didn't make his friend disappointed.

填空题