问题 选择题

在图中所示的电路中,电源电压保持不变。电路出现断路故障,故障可能发生在电阻R1、R2处,当电键S由断开到闭合时,

A.电压表V的示数一定变大

B.电流表A1的示数一定不变

C.电流表A2的示数可能变小

D.电压表V的示数可能变小

答案

答案:B

题目分析:①若电阻R1出现了断路故障,当电键S断开时,电压表测电源电压,由于电压表相当于开路,所以两电流表示数均为零,当电键S闭合时,电路中只有电压表连接在电源两端,电流表A1因电键S闭合被短路,没有示数;电压表测量电源电压;电流表A2测量电路电流,因电压表相当于开路,所以这时示数几乎为零;所以电压表示数不变,A错,两电流表示数都为零不变;②若电阻R2出现了断路故障,当电键S断开时,电路为断路,电压表电流表均为零,当电键S闭合后,电路中只有电阻R1连接在电源两端,电流表A1因R2断开,没有示数;电压表测量电阻R1两端的电压,即为电源电压;电流表A2测量通过电阻R1的电流;即电压表变大,电流表A1为零不变,电流表从零变为有示数也就是变大。所以答案选B。

阅读理解

Conor Grennan was unwilling to be a volunteer(志愿者). The 29-year-old American was not sure if he had the skills or a strong feeling for it.

However, he went to work at an orphanage(孤儿院) in Nepal. His first thought was to make people impressed.

"I thought that if I volunteered just once. I could retell the story over and over," Grennan said in a Huffington Post article.

However, his three-month stay it the orphanage turned into in unusual experience. It was 2004 and Grennan had given up his job to begin a year-long around-the-world trip, His first three months were spent in Nepal.

When he arrived in the village, he knew nothing about the children or the local culture. When he opened the gate of the Little Princes Children's Home, he was faced by the excited children.

The young American ended up caring for 18 children. He later discovered that they were trafficked(被拐卖的)children. So he walked through the mountains with great difficulty to find the kids' families, "I started walking with photos of the kids." he told the Reuters reporter. "I would show up in villages and show photographs around. I went with 24 photos, and I found 24 families."

At the same time, he put his heart into Nepalese culture.

Grennan said, “Volunteering is the single best way to see how the rest of the world lives.”

He also encouraged others to do what he had done. He believes that volunteering needs only making decisions to show up.

Grennan's fight against child-trafficking has changed him. His book, Little Prince, came out last week.

小题1:At first, Grennan simply wanted to _______by volunteering in Nepal.

A.write travel stories

B.learn the skills

C.help the kids there

D.impress people小题2:When Grennan came to the Little Princes Children’s Home. _______.

A.18 children were ill in bed

B.the children there felt excited

C.he decided to give up his job

D.he’d lived in Nepal for a year小题3:From the passage we can learn that Grennan _______.

A.found the kids’ families easily

B.was good at taking pictures

C.wrote the book Little Princes

D.asked others to go to Nepal小题4:Which is the best title for the passage?

A.Volunteer changes a lot

B.Volunteer is with the kids

C.Volunteer becomes a writer

D.Volunteer travels in Nepal

名词解释