问题 实验题

为了探究影响电热的因素,小伟设计了如图(1)所示电路,烧瓶中盛有质量、初温均相等的煤油,R>R

(1) 为了在较短的时间内达到明显的实验效果,选用煤油而不用水,主要是由于______.

(2) 通电一段时间后,比较两烧瓶中温度计的示数,是为了探究电热与_______的关系.

(3) 要利用此装置来探究电热与电流的关系,你还需要的操作是       _____________.

(4) 将此装置改装后可测量煤油的比热容,如图(2)所示.测量时,分别向两个相同的烧瓶中加入初温均为t0质量相等的水和煤油,通电一段时间后,分别读出温度计的示数为t、t煤油,请写出煤油比热容的表达式C煤油="__________" (已知水的比热容为C)(不计热量损失).

答案

(1)煤油的比热容小.(2)电阻.

(3)移动滑动变阻器滑片改变电流大小,比较通电时间相同时,甲(或乙)烧瓶中温度计的示数变化.

(4)

题目分析:(1)为了在较短的时间内达到明显的实验效果,选用煤油而不用水做实验,主要是由于水的比热容大于煤油的比热容,吸收相同的热量,温度变化不明显.

(2)已知通过两段电热丝的电流和通电时间都相同,所以此过程是研究电热与电阻大小的关系.

(3)要研究电热与电流的关系,必须移动滑动变阻器滑片,比较通电时间相同时,甲(乙)烧瓶中温度计的示数变化.

(4)在图中,两只烧瓶中的电热丝阻值相同,通过的电流相同,通电时间相同,所以水和煤油得到的热量相同,即

  

所以煤油的比热容为

点评:本题通过焦耳定律的实验重点考查学生对控制变量法、转化法的掌握和应用,以及学生分析实验现象得出结论的能力;控制变量法为物理实验中的常用方法,应重点掌握.

阅读理解

Now let’s talk about doing well by doing good—many people who have ever been volunteers for the community find their place in relative jobs or even make their way to be corporate(团体的)leaders.

Consider the case of Kimberly Mulcahy. Throughout her career, Mulcahy has actively volunteered in her community, profession and industry. Though she put in long hours as Vice President at a Fortune 500 company, she also found time to professional and community organizations.

Then last year, the unexpected thing happened. The company where she’d worked for more than 20 years was bought out and she was laid off.

On hearing the news, those who she served were quick not only to offer her support—but actual jobs! In the end, Mulcahy was hired by a PR agency—she used to work as a director of her industry association. And she brought with her several accounts based on relationships she had formed through volunteering.

Volunteering was a godsend(天赐之物)to Todd, who has been a mid-level manager at the same company for many years. After he was out of work, he felt old and disappointed. But Todd knew he needed a change. Todd became involved in community service. He joined his town’s volunteer fire department and was soon appointed to the finance committee.

Sometimes volunteering helps you bring passion to your work, other times it can turn your life’s passion into your work. Cape Cod Baseball League President Judy Scarafile is a registered pharmacist(药剂师)whose love of the game led her to volunteered as league publicist(宣传员), secretary and deputy commissioner woman to hold the top post.

Whether you are to enter the workforce, build your resume, or follow your passion, volunteering is good for the soul and the career.

小题1: By saying “doing well by doing good” in Paragraph 1, the author wants to_____.

A.encourage us just to do it, and it will be better

B.encourage us to try as hard as possible

C.tell us not to give up

D.tell us that people who have volunteered their way into小题2:Which of the following is NOT true about Mulcahy according to the passage?

A.Mulcahy put in long hours as Vice President at a Fortune 500 company.

B.Mulcahy becomes a famous football player.

C.Mulcahy brought with her several accounts based on relationships she had formed through volunteering.

D.Mulcahy was hired by a PR agency.小题3:Which of the following words can best describe Todd?

A.Learned

B.Lucky

C.Rude

D.Realistic小题4:Which of the following can be the best title for the passage?

A.Volunteer Work Can Boost Your Career.

B.Mulcahy’s Voluntary Work Experience.

C.It’s a Good Chance to Be a Volunteer.

D.Volunteer Work.

多项选择题