问题 实验题

如图,一热敏电阻RT放在控温容器M内:A为毫安表,量程6 mA,内阻为数十欧姆;E为直流电源,电动势约为3V,内阻很小;R为电阻箱,最大阻值为999.9 Ω;S为开关。已知RT在95℃时的阻值为150 Ω,在20℃时的阻值约为550 Ω。现要求在降温过程中测量在95 ℃~20 ℃之间的多个温度下RT的阻值。

(1)在图中画出连线,完成实验原理电路图。

(2)完成下列实验步骤中的填空:

①依照实验原理电路图连线;

②调节控温容器M内的温度,使得RT的温度为95 ℃;

③将电阻箱调到适当的初值,以保证仪器安全;

④闭合开关,调节电阻箱,记录电流表示数I0,并记录____________;

⑤将RT的温度降为T1(20 ℃<T1<95 ℃),调节电阻箱,使得电流表的读数____________,记录_______________;

⑥温度为T1时热敏电阻的电阻值RT1=________________;

⑦逐步降低T1的数值,直至20℃为止;在每一温度下重复步骤⑤、⑥。

答案

(1)

(2)④电阻箱的读数R0;⑤仍为I0,电阻箱的读数R1;⑥R0-R1+150 Ω

阅读理解

C

Holding a cell phone against your ear or storing it in your pocket may be dangerous to your health. This explains a warning that cell phone manufacturers include in the small print that is often ignored when a new phone is purchased. Apple, for example, doesn’t want iPhones to come closer to you than 1.5 centimeters; Research In Motion, BlackBerry’s manufacturer, recommends 2.5 centimeters.

If health issues arise from cell phone use, the possible effects are huge. Voice calls - Americans chat on cell phones 2.26 trillion(万亿)minutes annually - earn $109 billion for the wireless carriers.

Devra Davis, an expert who has worked for the University of Pittsburgh, has published a book about cell phone radiation, “Disconnect.” The book surveys scientific research and concludes the question is not settled.

Brain cancer is a concern that Ms. Davis examines. Over all, there has not been an increase in its incidence since cell phones arrived. But the average masks an increase in brain cancer in the 20-to-29 age group and a drop for the older population.

“Most cancers have multiple causes,” she says, but she points to laboratory research that suggests low-energy radiation could damage cells that could possibly lead to cancer.

Children are more vulnerable to radiation than adults, Ms. Davis and other scientists point out. Radiation that penetrates only five centimeters into the brain of an adult will reach much deeper into the brains of children because their skulls are thinner and their brains contain more absorptive fluid(易吸收的液体). No studies have yet been completed on cell phone radiation and children, she says.

Henry Lai, a research professor in the bioengineering department at the University of Washington, began laboratory radiation studies in 1980 and found that rats exposed to radiation had damaged DNA in their brains.

Ms. Davis recommends using wired headsets or the phone’s speaker. Children should text rather than call, she said, and pregnant women should keep phones away from the abdomen(腹部).

小题1:Why is the warning in the small print?

A.They think people will not care about it.

B.There is not enough space for the warning.

C.They don’t want the users to pay attention to it.

D.The warning is not important at all.小题2: What does the underlined word in sixth paragraph probably mean?

A.acceptable

B.valuable

C.accessible

D.easily affected小题3:What can we conclude from the last paragraph?

A.Pregnant women should keep cell phones away.

B.People should use cell phones in the correct way.

C.If you are a child, you’d better text than make phone calls.

D.When you use a cell phone, use a wired headset or the phone’s speaker.小题4: What does the passage mainly talk about?

A.Be careful when using cell phones.

B.Don’t hold your cell phone against your ear.

C.Rats exposed to radiation have damaged DNA in their brains.

D.Low-energy radiation could damage cells that could lead to cancer.

单项选择题