问题 计算题

电子体重秤的原理如图所示,R0为定值电阻,R是电阻值随所受压力大小发生变化的可变电阻,更换电压表(量程为0﹣3V)的表盘后可直接显示人体质量大小.已知R的电阻与所受压力F变化的关系如图象所示.设踏板的质量忽略不计,电源电压保持9V不变.(g=10N/kg)

(1)空载时,电压表的示数为1V,求R0的电阻值.

(2)该体重秤的量程是多大?

答案

(1)体重秤空载时受到的压力为0,由图象可知,此时电阻R=240Ω ,而电阻R0两端的电压为U1=1V,电源电压为U=9V,则R两端的电压为:U2=U﹣U1=9V﹣1V=8V,

∵  电阻R和定值电阻R0串联,∴此时电路中的电流为:I===A,

定值电阻的阻值为:R0===30 Ω;

(2)电压表示数最大为U1′=3V时,而R0=30 Ω,

∴此时电路中的电流为:I′===0.1A,

此时电阻R两端的电压为:U2′=U﹣U1′=9V﹣3V=6V,

∴此时电阻R的阻值为:R′===60 Ω,

由图象可知此时电阻R受到的压力为900N,在水平面上压力和重力相等,

∴体重秤的量程为:m===90kg.

单项选择题
阅读理解

(2013·高考新课标全国卷Ⅱ,C)Given that many people’s moods (情绪)are regulated by the chemical action of chocolate,it was probably only a matter of time before somebody made the chocolate shop similar to a drugstore of Chinese medicine.Looking like a setting from the film Charlie&the Chocolate Factory,Singapore’s Chocolate Research Facility (CRF) has over 100 varieties of chocolates.Its founder is Chris Lee who grew up at his parents’ corner store with one hand almost always in the jar of sweets.

If the CRF seems to be a smart idea,that’s because Lee is not merely a seasoned salesperson but also head of a marketing department that has business relations with big names such as Levi’s and Sony.That idea surely results in the imagination at work when it comes to making different flavored (味道) chocolates.

The CRF’s produce is “green ”,made within the country and divided into 10 lines,with the Alcohol Series being the most popular.The Exotic Series-with Sichuan pepper,red bean (豆),cheese and other flavors-also does well and is fun to taste.And for chocolate_snobs,who think that they have a better knowledge of chocolate than others,the Connoisseur Series uses cocoa beans from Togo,Cuba,Venezuela,and Ghana,among others.

小题1:What is good about chocolate?

A.It serves as a suitable gift.

B.It works as an effective medicine.

C.It helps improve the state of mind.

D.It strengthens business relations.小题2:Why is Chris Lee able to develop his idea of the CRF?

A.He knows the importance of research.

B.He learns from shops of similar types.

C.He has the support of many big names

D.He has a lot of marketing experience.小题3:Which line of the CRF produce sells best?

A.The Connoisseur Series.

B.The Exotic Series.

C.The Alcohol Series.

D.The Sichuan Series.小题4:The words “chocolate snobs” in Paragraph 3 probably refer to people who________.

A.are particular about chocolate

B.know little about cocoa beans

C.look down upon others

D.like to try new flavors