首页
登录
职称英语
Most sources of illumination generate light over an appreciable period, a
Most sources of illumination generate light over an appreciable period, a
游客
2024-01-05
75
管理
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://tihaiku.com/zcyy/3334808.html
相关试题推荐
Choose.TWOletters,A-E.WhichTWOsourcesoffundinghelpedbuildthefacility
Intheperiodbetween1918and1939,variouspolitical,economic,andgeographic
Mostsourcesofilluminationgeneratelightoveranappreciableperiod,a
Amasterisanelectronicapparatusthat______radioandlightwaves.A、generated
[originaltext]Nowwe’vebeentalkingabouttherevolutionaryperiodinthe
[originaltext]Nowwe’vebeentalkingabouttherevolutionaryperiodinthe
Theterm"iceage"referstoanyofseveralperiodsoftimewhenglacierscovere
"ResourcesandIndustrialisminCanada"→Whilethemuch-antici
"ResourcesandIndustrialisminCanada"→Whilethemuch-antici
"ResourcesandIndustrialisminCanada"→Whilethemuch-antici
随机试题
Questions29-40•ReadtheinformationbelowaboutMaureenDowd.•Choosetheco
OnlyafewhundredpeopleliveinYvoire,butthesmallvillageonthesouth
America’sCulturalCapital—ACenterreportthatcallsuponthePresident
Itisunfairforthosechildren______(只能接受较差的教育)simplybecausetheycan’taff
Infuturetradethekeydevelopmenttowatchistherelationshipbetweenthe
设备寿命的类型主要有()。A.更新寿命 B.物理寿命 C.折旧寿命 D
IEEE802.11MAC子层定义的竞争性访问控制协议是(),之所以不
房地产经纪业务( )是指房地产经纪机构和人员为推广业务与获得委托,让公众知悉、
下列关于工作满意度调查的描述,正确的是()。A:通过一定的手段和方法来调查员工对
按国际上的理解,下列属于咨询工程师的有()。A.结构工程师 B.建筑师
最新回复
(
0
)