问题 实验题

小刚同学学习了欧姆定律之后,想用电流表、电压表测量一段电阻丝R的电阻,他已连接了部分电路,如图所示,请你接着完成下列步骤:

(1)根据第(3)问,用笔画线代替导线,将电路补画完整

(2)连接电路过程中,开关应 _________ ,滑动变阻器的滑片应滑至使变阻器电阻 _________ (填“最大”、“最小”或“中间”)位置.

(3)当电压表示数为3.6V时,电流表的示数如图(b)所示,这时电路中的电流是 _________ A,电阻丝的电阻为_________Ω.小刚通过改变被测电阻两端的电压,共测得三组对应的电压值和电流值,最后算出电阻的平均值,这样做的目的是 _________

(4)若闭合开关后,无论怎样移动滑片,电流表几乎没示数,电压表示数约等于电源电压,则出现故障的原因可能是 _________ (选填下列序号)

A.滑动变阻接的两上或两下    

B.电阻丝R断路C.电阻丝R短路          

D.滑动变阻器连入电路的电阻太

(5)若将上面实验中的定值电阻R换成小灯泡,在多次测电阻的过程中,发现当电压表的示数增大时,电压表与电流表示数的比值将 _________

答案

(1)

(2)断开,最大;

(3)0.3,12,减小误差;

(4)B;(5)增大.

选择题
阅读理解

Parents are a child’s first teachers. But some parents never learned from good examples. In New York City, a nonprofit agency called Covenant House tries to help homeless young mothers become good parents.

The twelve or so teenagers who live at the shelter attend parenting classes four days a week. The class is called Mommy and Me. Teacher Delores Clemens is a mother of five and a grandmother. She teaches basic skills, like how to give a baby a bath and how to dress a baby depending on the season.

She remembers one student who learned from her mother not to pick up a crying baby. The mother said that would only make the child needy and overly demanding. Delores Clemens says, “that's not true. You have to hold your baby! He is crying for a reason. If you never pick him up, he's going to keep crying. Pick your baby up. Cuddle your baby. Hug him! And she started to do that. They just want a little cuddling and a little love. And it works!”

Delores Clemens says her students also learn how to be good mothers by letting themselves be mothered. Around three hundred fifty teenage mothers graduate from Covenant House's Mommy and Me class every year.

In class, with her baby son is Natasha. She lived on the streets. She is glad not only for the warmth and shelter of Covenant House. As she told reporter Adam Phillips, she is also glad for the help they offer in seeking a more secure life.

The World Health Organization says the United States has forty-one births for every one thousand girls age fifteen to nineteen. That is higher than other developed countries, as well as some developing ones. By comparison, northern neighbor Canada has fourteen births and southern neighbor Mexico has eighty-two.

小题1:What is the text mainly about?

A.Parents who are a child’s first teachers.

B.A class where teens learn mothering and are mothered.

C.A nonprofit agency that offers a more secure life.

D.A kind teacher who help homeless young mothers.小题2:Covenant Houses’ Mommy and Me class is intended to _____.

A.help homeless young mothers become good parents

B.provide homeless young mothers with a warm shelter

C.help mothers in New York be good parents

D.teach some parents how to love their children小题3:What can we know about Delores Clemens from the text?

A.She has a mother of five and a grandmother.

B.She thinks a crying baby should be picked up and hugged.

C.She teaches advanced skills on how to be good mothers.

D.She is very glad for the warmth and shelter of Covenant House.小题4: According to the World Health Organization, which country has the highest births for girls age fifteen to nineteen?

A.Canada

B.the United States of America

C.Mexico

D.Britain