问题 实验题

小虎同学利用注射器(容积为V)、弹簧测力计和刻度尺估测大气压的值.

(1)实验时.首先把注射器的活塞推至注射器筒的底端,用橡皮帽封住注射器的小孔,这样做的目的是_____________________.

(2)如图所示,水平向右慢慢地拉动注射器筒.当注射器中的活塞刚开始滑动时,记下弹簧测力计的示数F.用刻度尺测出注射器全部刻度的长度L.则大气压的值可以表示为p=_______.

(3)实验过程中注射器筒内漏进了少量空气,则测得的大气压值_______(偏大/不变/偏小).

(4)实验室有甲、乙两个注射器.活塞的横截面积分别为0.5cm2和2cm2.若弹簧测力计量程为10 N,实验时应选用_______(甲/乙)注射器,理由是_______.

答案

(1)排尽注射器筒内空气  (2)(3)偏小  (4)甲  若选择乙注射器,则拉力会超过弹簧测力计的量程

题目分析::(1)实验时,把活塞推至注射器筒底端是为了排出注射器中的空气.

(2)当注射器中的活塞开始滑动时,弹簧测力计的拉力与大气的压力刚好平衡,因此需要记录此时的示数;注射器是一个圆柱体形状,因此,应量出其刻度部分的长度,再读出空积V,得出活塞的面积

将测量结果代入压强公式得:

(3)如果筒内空气没有排尽,拉力的测量值会偏小,根据公式可知,导致测得的大气压值偏小;相反,如果活塞与注射器内壁间的摩擦较大,拉力的测量值会偏大,导致测得的大气压值偏大.

(4)因甲、乙两个注射器,活塞的横截面积分别为0.5cm2和2cm2

当大气压约为100000Pa,当面积为2cm2,即0.0002m2时,

,可得F=PS=100000Pa×0.0002m2=20N,

因为已知弹簧测力计量程为10N,超过了测力计的量程,

所以实验时应选用甲注射器,

故理由是拉动乙注射器所需的力超过弹簧测力计的量程.

点评:利用注射器测量大气压时,用到的公式是所以要分别测大气压力F和活塞的横截面积S.利用二力平衡可通过弹簧测力计测出大气压力,利用几何知识可得出活塞的面积S,便可求出大气压的值了.对测量结果的评估则主要看是否对几个测量值造成了影响,造成了怎样的影响,最后确定是偏大或偏小.

阅读理解

Green is an important color in nature. It is the color of grass and the leaves on trees. It is the color of most growing plants, too.

Sometimes, the word green means young, fresh and growing. Sometimes, it describes something that is not yet finished or plants that are not ripe.

For example, a greenhorn is someone who has no experience, who is new to a situation. In the fifteenth century, a greenhorn was a young cow or ox whose horns had not yet developed. A century or so later, a greenhorn was a soldier who had not yet had any experience in war (战争). By the eighteenth century, a greenhorn had the meaning it has today--a person who is new in a job.

About one hundred years ago, greenhorn was a popular expression in the American west. Old-timers used it to describe a man who had just arrived from one of the big cities in the east. The greenhorn didn’t have the skills that he would need to live in the hard, rough country.

Someone who has the ability to grow plants well is said to have a green thumb. The expression comes from the early nineteen hundreds.

A person with a green thumb seems to have a magic touch that makes plants grow quickly and well. You might say that the woman next door has a green thumb if her garden continues to grow long after your plants have died.

The Green Revolution (革命) is the name which was given some years ago to the development of new kinds of rice and other grains. The new plants produced much larger crops. The Green Revolution was the result of hard work by agricultural (农业的) scientists who had green thumbs.

小题1:According to the passage, a greenhorn means________ now.

A.a young cow or ox whose horns have not yet developed

B.a soldier who has not had any experience in war

C.a person who is new in a job

D.a man who doesn’t have the skills to live in the country小题2:The meaning of the underlined word “ripe” in the second paragraph is ________.

A.未完成的

B.成熟的

C.青涩的

D.老练的小题3:Which of the following about the Green Revolution is NOT right?

A.If there weren’t the Green Revolution, we would have no rice to eat.

B.The expression “the Green Revolution” appeared several years ago.

C.Because of the Green Revolution, we have more kinds of rice and other grains.

D.Agricultural scientists with green thumbs started the Green Revolution.小题4:We can know from the passage that _______.

A.all growing plants is green

B.green is the most important color in nature

C.a person with a green thumb can make plants grow well

D.the expression “a green thumb” has a history of two hundred years小题5:The main idea of the passage is ________.

A.a greenhorn

B.a green thumb

C.the Green Revolution

D.the word “green” and its story

单项选择题 A1/A2型题