首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Most sources of illumination generate light over an appreciable period, and indeed if an object is lit for a very brie
Most sources of illumination generate light over an appreciable period, and indeed if an object is lit for a very brie
admin
2005-01-30
90
问题
Most sources of illumination generate light over an appreciable period, and indeed if
an object is lit for a very brief time(less that 1/25 second), the human eye will not react
in time to see the object. A photographic emulsion---that is, a light-sensitive coating on
photographic film, paper, or glass--will, however, record much shorter bursts of light. A
(5) photographic flash can therefore be used to capture high-speed movement on film as well
as to correct deficiencies of the normal surrounding lighting. Photoflash is now generated
electronically, but the earliest form, first used in 1864, was a paper bag containing
magnesium wire and some oxygen-rich substance, such as potassium chlorate. When the
bag was ignited, the metal burned with an intense flash. A contemporary observer reported
(10) that "this quite unsafe device seems to have done nothing worse that engulf the room in
dense smoke and lead to pictures of dubious quality and odd poses."
The evolution of the photoflash was slow, flashbulbs, containing fine wire made of a
metal, such as magnesium or aluminum, capable of being ignited in an atmosphere of pure oxygen
at low pressure, were introduced only in the 1920’s.In the earliest type, the metal
(15) was separated from the oxygen by a thin glass bulb. The dash was fired by piercing the
bulb and allowing the oxygen to come into contact with the metal, which ignited
spontaneously. Later bulbs were fired by an electric battery, which heated the wire by
passing a small current through it. Other combinations, such as the pairing of oxygen
difluoride with zirconium, have also been used. In each case enough energy is given out to
(20) heat the oxidizable metal momentarily to a white-hot emission of visible light. The smoke
particles are so small that they cool rapidly; but since they are white, they contribute to the
brilliance by reflecting the light from their still-glowing neighbors. A slightly bigger form
of the metal will burn for a longer time.
选项
A、The history of the photoflash
B、Theories about how the eye reacts to light
C、The technology of modern photography
D、The dangers of using the early photoflash
答案
A
解析
转载请注明原文地址:https://www.kaotiyun.com/show/bIyO777K
0
托福(TOEFL)
相关试题推荐
Youshouldspendabout20minutesonQuestions1-13,whicharebasedonReadingPassage1below.Sustainablearc
Youshouldspendabout20minutesonQuestions15-27.MinnesotaDepartmentofNaturalResources(DNR)Volunteerin
EarlyoccupationsaroundtheriverThamesAInherpioneeringsurvey,SourcesofLondonEnglish,Laura
WilliamGilbertandMagnetismA16thand17thcenturiessawtwogreatpioneersofmodernscience:GalileoandGilbert.Theimpac
CommunicatingStylesandConflictKnowingyourcommunicationstyieandhavingamixofstylesonyourteamcanprovideapositiv
CommunicatingStylesandConflictKnowingyourcommunicationstyieandhavingamixofstylesonyourteamcanprovideapositiv
InwhichyeardidtheSPIintroducetherecyclingsymbol?
Completethesentencesbelow.WriteNOMORETHANTWOWORDSforeachanswer.JobsatisfactionstudyThevarioussub-groupswere_
Completethenotesbelow.WriteONEWORDONLYforeachanswer.GRAPHICALSYMBOL’Graphicalsymbol’includesthelogographsi
CancerandChemicalsLastyear,CaliforniagovernorGeorgeDeukmejiancalledtogethermanyofthestate’sbestscientificmi
随机试题
男性,43岁,因头痛伴呕吐、双眼视物不清4个月收入院。查体:意识清醒;视力:左眼前数指,右大致正常;眼底:左视乳头边清色淡,右视乳头边缘不清、乳头隆起2D。为明确诊断,首先应安排的检查是
某高速公路隧道长度为3200m,年平均日交通流量为8000pcu/d,其定期检查结果如下:①洞门拱部及其附近部位出现剥落,壁面存在严重渗水和挂冰,将会妨碍交通;②衬砌存在较多裂缝,但宽度变化较小,边墙衬砌背部存在空隙,有扩大可能;③路面大面积的明显沉
下述沉入桩的打桩顺序中,正确的有(),
国际工程投标报价的动态分析,主要考虑工期、物价和工资上涨以及其他可变因素的影响。下列属于工期延误的影响因素是()。
主张学生自发地决定学习目的和学习内容,并据此组成学习单元,自己设计、自己负责执行的教学组织形式为()。
阅读下列材料,回答问题。①来时,便听说台北是个多雨的城市,尤其是冬季,雨下得更是非同凡响,为世界上许多城市所不能比。我不是专门到台北来看雨的,我从家乡来,我说家乡话,我唱家乡戏,我带着家乡情来看家乡人。为两岸的文化交流,我们一行20人,应台湾名伶
下列是普通高中课程标准实验教科书必修《数学》第四册(人教版)关于“简单的三角恒等变换”的部分教学内容,请阅读并据此回答问题。例2.求证:(1)sinαcosβ=[sin(α+β)+sin(α-β)];(2)sinθ+sinφ=2sin证明:(1)因为
从0,1,2,…,9这十个数字中任意选取三个不同的数字,则三个数字中不含0或5的概率为
TheBeatles甲壳虫乐队TheEnglishrockmusicgroupTheBeatlesgavethe1960sitscharacteristicmusicalflavorand(1)aprofoun
A、Heisapostraduate.B、Heisqualifiedforteachingpostgraduates.C、Heisanexpertintownplanning.D、Hehasonlygivenone
最新回复
(
0
)