分压法在串联电路中的应用

串联电路又叫分压电路,是把电源电压分配给串联的各个电阻.由于在串联电路中,各电阻两端的电压与其电阻值成正比,因此,在电源电压不变的情况下,串联的电阻越大,分得的电压就越多;电阻越小,分得的电压就越少.现举例说明它的应用.     

解读欧姆定律与考点分析

一、重点难点突破1.电阻上的电流跟两端电压和电阻有什么关系在探究电阻上的电流跟两端电压和电阻的关系这个实验中,我们研究的是电流与电压和电阻的关系,所以要控制电阻或电压不     

怎样消除伏安法在测试电阻实验中的系统误差

伏安法测电阻实验是电学中一个重要实验,其原理是测出待测电阻两端的电压及通过待测电阻的电流,利用部分电路欧姆定律求出待测电阻的阻值。但是在实际测量时由于电流表、电压表内阻的影响,我们不能同时测出待测电阻两端电斥和通过其电流的真实值,所以测量结果存在一定的系统误差。虽然我们可以估算待测电阻的大小而采用电流表内接法或外接法,     

专题19 电阻等效方法

计算一个电路的电阻，通常从电路的欧姆定律出发，对电阻串联构成的电路，电流为I，则IR=IR1＋IR2＋…；对电阻并联构成的电路，两端电压为U，则U/R=U/R1＋U/R2＋…，于是得到串联电路的等效电阻为各个串联电阻之和，并联电路的等效电阻为各个并联电阻的调和平均．实际电路中，电阻的连接是千变万化的，这需要我们运用各种技法，     

非线性元件问题的分析

如果加在电路元件两端的电压跟通过元件电流的比值--电阻不是常数,而是随着所加电压的变化而变化,则此元件就称为非线性元件.如白炽灯泡实际上就属于此类元件,它的电阻并非是一个常数,只是在平时所遇到的习题中把它进行了理想化处理,认为灯丝的电阻不变.     

电压和电阻重难点指要

一、知基点--电压和电阻 要在一段电路中产生电流.它的两端就要有电压,电压的作用是使电路中产生电流.电源是提供电压的装置.测量电压的工具是电压表,它测量的是某一段电路或某一个用电器两端的电压.导体对电流的阻碍作用叫做电阻.规定如果导体两端的电压是1V,通过导体的电流是1A,则这段导体的电阻是1Ω.     

浅析对《生活用电常识》中的两个误解

如果加在电路元件两端的电压跟通过元件电流的比值——电阻不是常数,而是随着所加电压的变化而变化,则此元件就称为非线性元件。如白炽灯泡实际上就属于此类元件,它的电阻并非是一个常数,只是在平时所遇到的习题中把它进行了理想化处理,认为灯丝的电阻不变。     

分压公式在动态电路中的应用

如图1,在串联电路中,导体两端的电压与电阻成正比,即U1/U2=R1/R2,     

直流电路中含电容电路的求法

在直流电路中,充电完毕后的电容器处于断路状态,这是我们解决含电容电路的前提。由于电容器充电完毕后处于断路状态,因此和电容器串联的电阻上由于电流为零而两端的电势相等,这样我们就可以用一无阻导线将该电阻替换掉,文中讲了这种情况下解题的几种方法。     

关于电路变化问题的定性分析

在初中物理的电学习题中，经常会遇到这样一类问题：电源电压不变，由于可变电阻阻值变化，或者说某个开关闭合或断开引起阻值变化，然后让你判断电路的电流、各电阻两端的电压以及电功率怎样变化，学生对这样的问题感到非常棘手．其实这是有规律可循的，首先弄清电路的串并联关系，然后根据电压、电阻、电流间的变化关系，在寻找变量的同时，要注意哪些是不变的物理量，便可以顺利解决问题，因为电阻、     

参考文献在正文中的标注位置及其与相关标点符号的关系

研究参考文献在正文中的标注位置问题，可以分为两种情况：一种是文献序号只和点号连用，这种情况标注位置比较单一，便于操作；另一种情况是引文引号、点号、文献序号三者连用。这种情况标注位置比较复杂，要求分清结构。辩明语气正确理解句子的意义，才能安排好三者的位置，准确表达文意，以便读者更进一步地了解文章。参考文献在正文中标注位置的规范化及正确与否，是科技期刊的质量、科技论文的学术水平极有说服力的测度。     

遵义方言的数词

遵义方言的数词可分为基数词、概数词和序数词。文章讨论遵义方言数词 ,兼及本方言基数、概数、序数表达的习惯格式     

Using order to reason about negative numbers: the case of Violet

This case study illustrates how a 2nd-grade child, Violet, used an ordinal view of number to reason about positive and negative integers and arithmetic involving integers. Violet’s ordinal view of number facilitated her ability to reason about and correctly solve some integer-related problems and constrained her solutions to others. We demonstrate how Violet’s thinking evolved over time while she extended the properties of whole numbers and addition and subtraction to the integers. Using this case study as a basis, we propose a series of developmental milestones that build toward one’s understanding of integers and integer arithmetic in an order-based way. We believe that understanding Violet’s order-based reasoning can help us listen to other children.     

5～6岁儿童对数的理解能力的发展

对数字的认识和理解可以看成是儿童数学学习的开始,本文通过问卷调查等方法,对5～6岁儿童的学习内容、方法和过程等进行调查,调查发现学前儿童对数的顺序关系、数的基数特点、序数特点以及数的抽象含义等内容能有较好的理解。     

线性应变增量最佳值的确定

经过分析得知 ,在线性范围内采用等值增量法加载 ,试件上各测点的应变 ε与加载序数 n成线性关系 .因此 ,应用最小二乘法可以拟合一条最佳直线 ,进而确定应变增量Δε的最佳值     

Longitudinal Models for Ordinal Data With Many Zeros and Varying Numbers of Response Categories

Ordinal response scales are often used to survey behaviors, including data collected in longitudinal studies. Advanced analytic methods are now widely available for longitudinal data. This study evaluates the performance of 4 methods as applied to ordinal measures that differ by the number of response categories and that include many zeros. The methods considered are hierarchical linear models (HLMs), growth mixture mixed models (GMMMs), latent class growth analysis (LCGA), and 2-part latent growth models (2PLGMs). The methods are evaluated by applying each to empirical response data in which the number of response categories is varied. The methods are applied to each outcome variable, first treating the outcome as continuous and then as ordinal, to compare the performance of the methods given both a different number of response categories and treatment of the variables as continuous versus ordinal. We conclude that although the 2PLGM might be preferred, no method might be ideal.     

3～5岁幼儿数概念的发展

从给物说数、比较多少、圆点排序和选序数4个方面探查30名3~5岁的幼儿数概念（包括基数和序数）的发展。研究结果表明：（1）幼儿对数概念的掌握随年龄增长而提高,其中4~5岁是幼儿数概念发展的关键期;（2）幼儿对基数和序数的掌握显示出不同的发展速度,基数发展在先;（3）幼儿数概念的发展不存在性别差异。     

Comparing the Fit of Item Response Theory and Factor Analysis Models

Linear factor analysis (FA) models can be reliably tested using test statistics based on residual covariances. We show that the same statistics can be used to reliably test the fit of item response theory (IRT) models for ordinal data (under some conditions). Hence, the fit of an FA model and of an IRT model to the same data set can now be compared. When applied to a binary data set, our experience suggests that IRT and FA models yield similar fits. However, when the data are polytomous ordinal, IRT models yield a better fit because they involve a higher number of parameters. But when fit is assessed using the root mean square error of approximation (RMSEA), similar fits are obtained again. We explain why. These test statistics have little power to distinguish between FA and IRT models; they are unable to detect that linear FA is misspecified when applied to ordinal data generated under an IRT model.     

Collapsing Categorical Variables and Measurement Invariance

Cross-cultural comparisons of latent variable means demands equivalent loadings and intercepts or thresholds. Although equivalence generally emphasizes items as originally designed, researchers sometimes modify response options in categorical items. For example, substantive research interests drive decisions to reduce the number of item categories. Further, categorical multiple-group confirmatory factor analysis (MG-CFA) methods generally require that the number of indicator categories is equal across groups; however, categories with few observations in at least one group can cause challenges. In the current paper, we examine the impact of collapsing ordinal response categories in MG-CFA. An empirical analysis and a complementary simulation study suggested meaningful impacts on model fit due to collapsing categories. We also found reduced scale reliability, measured as a function of Fisher’s information. Our findings further illustrated artifactual fit improvement, pointing to the possibility of data dredging for improved model-data consistency in challenging invariance contexts with large numbers of groups.     

主族元素族序数的快速推断法--元素周期律周期表教学一则

以原子序数大小为依据,分为原子序数≤9、10≤原子序数≤79、原子序数≥80的三种情况,阐述了推断主族元素族序数的方法,揭示了元素周期表主族元素位置排列的另一规律.