问题 选择题

用图所示的电路探究半导体的导电性能,电路中电源电压不变,R是一只光敏电阻,当光照射强度增大时,其电阻会减小,闭合开关,减小光敏电阻的照射强度,电压表和电流表示数的变化情况是(  )

A.电流表、电压表示数均减小

B.电流表、电压表示数均增大

C.电流表示数增大、电压表示数减小

D.电流表示数减小、电压表示数增大

答案

因光照射强度增大时,其电阻会减小;

所以,减小光敏电阻的照射强度时,光敏电阻阻值增大;

则由欧姆定律I=

U
R
可知,电源电压不变,则电路中电流减小;

即电流表示数减小.

根据欧姆定律U=IR可知:灯泡的阻值不变,通过灯泡的电流变小,则灯泡两端的电压减小;

再由串联电路的电压规律可知,光敏电阻两端的电压及灯泡两端的电压之和等于电源电压,因电源电压不变,灯泡两端的电压减小,则可知光敏电阻两端的电压增大;

即电压表示数增大.

故选D.

阅读理解

The day was Thankful Thursday. It's a weekly tradition that my two little girls and I began years ago. Thursday has become our day to go out and make a positive contribution. On this particular Thursday, we had no idea exactly what we were going to do. At noon, I drove to a McDonald’s with my daughters because they kept complaining that they hadn’t had enough to eat at breakfast. There we saw some homeless people in the street and we bought lunch for them.

We were about to complete when we found a small woman standing at the corner, asking for change. We handed her some food, and then started to head home. Suddenly from the mirror of the car, I saw the woman waving at us, so I had to turn around and stopped where the small woman stood. She walked to our car, and said, "Thank you, lady! No one has ever done anything like this for me before." I replied, "Well, I'm glad that we were the first." Feeling uneasy, and wanting to move the conversation along, I asked, "So, when do you think you'll eat your lunch?"

She just looked at me with her huge, tired brown eyes and said, "Oh honey, I'm not going to eat this lunch." I was confused, but before I could say anything, she continued. "You see, I have a little girl of my own at home and she just loves McDonald's, but I can never buy it for her because I just don't have the money. But you know what…tonight she is going to have McDonald's!"

I don't know if the kids noticed the tears in my eyes. So many times I had questioned whether our Acts of Kindness were too small to have effect on those poor people. Yet at that moment, I realized the truth of Mother Teresa's words: "We cannot do great things — only small things with great love."

小题1:

According to this passage, the small woman was ______.

A.too happy to stand at the corner

B.too eager to ask for more food

C.too poor to buy McDonald’s

D.too busy to care for her daughter小题2:

What can we know from the passage?

A.The author finally realized what she did was of use to the poor.

B.The author would stop doing her acts of kindness to the poor.

C.The author’s daughters found their mother cried at the end of the day.

D.The author’s daughters would make friends with the woman’s daughter.小题3:

What would be the best title of the passage?

A.No Pains No Gains

B.No Pleasure Without Pain

C.No Small Act of Kindness

D.No Sweet Without Sweat

填空题