问题 实验题

(9分)(1)为了测量电源的电动势和内阻,我们通常采用如图甲所示电路,请根据甲电路图连接实物图。

(2)由于电压表和电流表内阻的影响,采用甲电路测量存在系统误差,为了消除这一影响,某同学选择两块量程合适的电压表V1、V2,一个满足实验要求的电阻箱R和三个开关,并设计了如图乙所示的测量电路,进行了如下的主要测量步骤:

①闭合S2,断开S1、S3,记下V1和V2的示数U1和U2

②断开S2、闭合S3,S1仍断开,调节电阻箱R,使电压表V2的示数仍为U2,读出电阻箱的阻值为R0

③闭合S1、S2,断开S3,记下V1的示数

请利用以上的测量物理量的字母写出电压表V1内阻表达式=______,该电源的电动势和内阻的测量值表达式E=______,r=______。

答案

(1)电路图连接如图

(2)                

题目分析:(1)电路图连接如下图;

(2)设电压表V1、V2的电阻为Rv1、Rv2,由题中条件可知;当闭合S2,断开S1、S3时,由闭合电路欧姆定律,可得;当闭合S1、S2,断开S3时,由闭合电路欧姆定律,可得,联立以上各式,解得

单项选择题

Pretty in pink: adult women do not remember being so obsessed with the colour, yet it is pervasive in our young girls’ lives. It is not that pink is intrinsically bad, but it is such a tiny slice of the rainbow and, though it may celebrate girlhood in one way, it also repeatedly and firmly fuses girls’ identity to appearance. Then it presents that connection, even among two-year-olds, between girls as not only innocent but as evidence of innocence. Looking around, l despaired at the singular lack of imagination about girls’ lives and interests.

Girls’ attraction to pink may seem unavoidable, somehow encoded in their DNA, but according to Jo Paoletti, an associate professor of American Studies, it is not. Children were not colour-coded at all until the early 20th century: in the era before domestic washing machines all babies wore white as a practical matter, since the only way of getting clothes clean was to boil them. What’s more, both boys and girls wore what were thought of as gender-neutral dresses. When nursery colours were introduced, pink was actually considered the more masculine colour, a pastel version of red, which was associated with strength. Blue, with its intimations of the Virgin Mary, constancy and faithfulness, symbolised femininity. It was not until the mid-1980s, when amplifying age and sex differences became a dominant children’s marketing strategy, that pink fully Came into its own, when it began to seem inherently attractive to girls, part of what defined them as female, at least for the first few critical years.

I had not realised how profoundly marketing trends dictated our perception of what is natural to kins, including our core beliefs about their psychological development. Take the toddler. I assumed that phase was something experts developed after years of research into children’s behaviour: wrong. Turns out, according to Daniel Cook, a historian of childhood consumerism, it was popularised as a marketing trick by clothing manufacturers in the 1930s.

Trade publications counselled department stores that, in order to increase sales, they should create a "third stepping stone" between infant wear and older kids’ clothes. It was only after "toddler" became a common shoppers’ term that it evolved into a broadly accepted developmental stage. Splitting kids, or adults, into ever- tinier categories has proved a sure-fire way to boost profits. And one of the easiest ways to segment a market is to magnify gender differences—or invent them where they did not previously exist.

According to Paragraph 2, which of the following is true of colours()

A. Colours are encoded in girls’ DNA

B. Blue used to be regarded as the colour for girls

C. Pink used to be a neutral colour in symbolising genders

D. White is prefered by babies

单项选择题