小议电学实验中仪器的选择

电学实验中仪器的选择是一项综合性指标,既要对仪器不造成损害,又要使测量的误差尽可能的小,并不是量程不小于待测量值和实际值不大于额定值即可。怎样选择仪器呢? 一、电表的选择指针式电压表、电流表的“允差”(最大可能误差)为±(量程×等级÷100),例如某一2.5级电压表量程0～3伏,允差ΔU=±3×2.5％=±0.075伏。因此,用同一量程时,电表不同示数的绝对误差相同,但相对误差不同。当上述电压表读数U=2.5伏时,则相对误差仍为ΔU/U=±0.075/2.5=±3％,而当读数U=0.50伏时、相对误差却增大为ΔU/U=±0.075/0.50=±15％。由此可见,选择电表量程时,应使指针的偏     

《工程检测技术》习题答案及选解

〔习题3-1〕(1)算术平均误差:δ_Ⅰ=3.6、δ_Ⅱ=3.6;(2)标准偏差:σ_Ⅰ=3.9、σ_Ⅱ=6.2。〔习题3-2〕无周期性系统误差,无累进性系统误差。〔习题3-3〕(1)串联总电阻:R_串=5000Ω、绝对误差±5Ω,相对误差0.1％;(2)并联总电阻:R_并=200Ω,绝对误差±0.2Ω,相对误差0.1％。〔习题3-4〕相对误差3.2％。〔简解〕(1)测50mV时,毫伏表的基本误差为:γ_1=仪表满量程示值/测量值×仪表引用误差=100/50×1.5=3％;(2)温度附加误差:     

用分数方法求几何图形面积几例

在小学阶段,有些几何图形的面积引导学生用分数方法解答既简便,又利于学生掌握,而且突出了图形之间的相互关系,培养了学生良好的思维品质。下面举例说明。在教学中,我们可以发现:圆心角是90°的扇形面积是以它的半径为边长的正方形面积的78.5％。(π取3.14) 证明:圆心角是90°的扇形的半径为r,则面积是πr~2×(90)/(360)=πr~2/4。边长为a的正方形面积为a~2。当a=r时,则a~2=r~2,扇形面积是正方形面积的(πr~2)/(4/a~2),当π取3.14时,则π/4=0.785=78.5％还可以得出图中阴影部分面积为1-78.5％=     

高效液相色谱法同时测定奶粉或饲料中的三聚氰胺和三聚氰酸

食品或饲料中三聚氰胺和三聚氰酸经乙腈水萃取、提纯后,采用高效液相色谱(HPLC)法测定,外标法定量.对色谱分离条件进行了优化,三聚氰胺在0.1156～11.56 mg/L范围内线性良好,复相关系数r2=0.9997,平均加标回收率在95.59％～105.97％之间,相对标准偏差为0.14％～0.29％,检出限(S/N=3)为0.012 mg/L.三聚氰酸0.1020～10.20mg/L范围内线性良好,复相关系数为r2=0.9995,平均加标回收率在77.44％～88.77％之间,相对标准偏差为0.32％～0.86％,检出限(S/N=3)为0.051 mg/L.该法能满足食品或饲料中三聚氰胺和三聚氰酸检验工作的需要.     

原子荧光光谱法测阴地蕨的硒含量

采用氢化物发生—原子荧光光谱法测定了阴地蕨根和叶中的硒含量.结果表明,硒含量在0～10ng/mL之间线性关系良好,其相关系数r=0.9996,其回归方程为y:140.02x+27.回收率为98.9％～101％,相对标准偏差RSD=0.73％,检出限为1.45ng/g;硒在阴地蕨全草中分布比较均匀.该方法具有准确度较高、重现性好和线性范围宽的优点.     

有关混和溶液浓度解题规律例谈

例 1将溶质质量分数为 3p％的某溶液与 p％的该溶液等体积混和后,其溶质质量分数小于 2p％,则这种物质可能是 A H2SO4 B氨水 C NaOH D C2H5OH 解析： 设 3p％的密度为ρ 1, p％的密度为ρ 2,体积均为 V,混和溶液的密度为ρ,则混和溶液溶质质量分数： =× 100％ =％ =％ =2p％＋ p％ 由上式可知,当浓度与溶液的密度成正变关系时,ρ 1－ρ 2>0,则混合后溶质质量分数大于其算术平均值;若浓度与溶液的密度正反变关系时,ρ 1－ρ 2 大家知道,已知溶液的溶质质量分数为 a％,密度为ρ g/cm3,则其物质的量浓度为： …     

海洛因依赖者时间管理倾向与自我价值感的相关研究

目的探讨海洛因依赖者的时间管理倾向与自我价值感的特点及二者的关系。方法运用时间管理倾向量表和自我价值感量表对150名海洛因依赖者进行问卷调查。运用均值差异性检验、方差差异分析、相关分析及多元逐步回归分析。结果 1.海洛因依赖者的时间管理倾向显著低于大学生;2.海洛因依赖者自我价值感高于常模群体;3.海洛因依赖者时间管理倾向和自我价值感有显著正相关;4.时间价值感和时间监控观对自我价值感有预测作用,但未发现时间效能感对自我价值感有预测作用,表现出特殊性。结论海洛因依赖者的时间管理倾向、自我价值感同常模有差异,海洛因依赖者的时间管理倾向与自我价值感呈显著正相关。     

等比定律在化学计算中的应用

1 等比定律(一) 1.1 若有a/b=a'/b'(设a相似文献   

掌握规律预防早 常见错误不常见

不少小学数学教师在教学的实践中,发现一个奇怪又极为普遍的现象:不同学校,甚至不同年代的学生,在学习数学的某一阶段出现的一些错误,几乎是完全相同的。比如:0.5小时=50分,80×0=80,3/4+3/4=6/8,0.8999>0.9,7-3(1/2)=4(1/2),100增加10％,再减少10％,仍然是100,等等。这些错误一般发生在那些对知识不求甚解的学生身上,而且很不容易纠正。     

百分数“病例”诊治

[病例1]因为1/2=50％,所以1/2千克=50％千克。     

卡思卡特城堡

It is worthy of noting that, whilst Crookston Castle witnessed the earlier and happier portion of Mary's variegated life,     

不同的吃喝玩乐

一、吃和喝吃苹果 eat an apple, 吃药 take medicine,吃糖 have some sweets,吃饭 have one's meals,吃馆子 dine out,吃惊 be surprised/     

漏洞百出的教育

Many college freshmen arrive woefully unprepared to do college work, and as disadvantaged populations continue to grow, the share of the American work force that has made it through college is expected to plummet. Many experts blame that educational failure not just on high schools but also on colleges. School & College, a special report by The Chronicle, looks at efforts to fix the system. What reforms would better prepare students for college? What should schools and colleges be doing differently? How should state and federal officials help?     

只要努力,不要后悔

There are numbers of crossroads on our long and unpredictable life journey where we totally have no idea about which direction to choose. No matter what our decision is, we should not turn back, but face the music and go ahead instead. I am this kind of girl who always does try without regretting, one example is how I dealt with my love.     

浅谈移民问题

Migration occurs behind a variety of reasons and has a great effect on the whole world. People may migrate in order to improve their economic situation, or in order to escape civil strife, persecution, and environmental disasters. The impact of migration is complex, bringing both benefits anddisadvantages. This paper briefly talks about the causes of migration, the allocation of benefits, and the ways in which individual countries and the international community deal with this important subject.     

Sister Carrie, an Adherent of Desires

Sister Carrie is one of the most controversial characters in American literature.Thought as a "fallen woman" firstly,she was defined as a "new woman" by some critics later. However, by digging into the motivaton behind the whole process of Carrie's "success", the relationship between Carrie and her creator (the author), the social conditions of then American, it can be found that Carrie has never been free-standing on her thought and she has never found her real-sdf even after becoming a famous actress. In a society dominated by mass consumerism Carrie is only an adherent of her own desires. She also is a representative of all those country girls flooded into cities, a symbol and a sacrifice of the urbanization of America in a time countryside was overcome by cities.     

Improvement of one-cycle controller by use of proportional integral differential controller

1.IntroductionOne-cyclecontrolmethod,whichwasproposedaboutonedecadeago[1],hasbecomeanattractivemethodinspecialfieldssuchaspowerfactorcorrection[2-6],switchingamplifiers[7,8],etc.Themainideaofthiscontrollerisbasedonintegrationofdiodevoltageinone-cycleandforcesittobeexactlyequaltothereferencevalue.Themainadvantageofthiscontrollerisitsrealtimeabilitytorejectthevariationofinputvoltage[1].Despitethisgreatability,ithasnogoodperformancesinrejectingofloaddisturbanceandfollowingreferencecommands.Espec…     

库克斯顿城堡

城堡, 是欧洲典型的建筑之一, 每个城堡都有一个美丽的传说或是一段历史。从本期开始, 我们将推出“城堡之旅”, 带各位读者去浏览、观赏欧洲各地的城堡, 开始一段文化与历史的旅途!     

The Reader Response Approach to Teaching of English Literature

During interview with English majors, it was found that a majority of students expressed disappointment with their experience of English literature classes. Students' dislike of learning English literature appears to be the major problem of teaching English literature in China. Reader response approach is a good way to solve this problem. In this paper, I explain the rationale behind the reader response approach, such as its origin, definition, features, assumptions, and strategies. Then I illustrate how reader response approach works as a teaching strategy by presenting several teaching models. At last I evaluate its usefuiness for teachers and present the advantages of reader response approach in Chinese context.