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
2025-02-09
29
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/3949368.html
相关试题推荐
Mostsourcesofilluminationgeneratelightoveranappreciableperiod,a
Thetwentiethcenturyhasbeenaperiodofenormousgrowthinmathematicalresea
[originaltext]Nowwe’vebeentalkingabouttherevolutionaryperiodinthe
Theterm"iceage"referstoanyofseveralperiodsoftimewhenglacierscovere
"ResourcesandIndustrialisminCanada"→Whilethemuch-antici
"ResourcesandIndustrialisminCanada"→Whilethemuch-antici
"ResourcesandIndustrialisminCanada"→Whilethemuch-antici
"ResourcesandIndustrialisminCanada"→Whilethemuch-antici
"ResourcesandIndustrialisminCanada"→Whilethemuch-antici
"ResourcesandIndustrialisminCanada"→Whilethemuch-antici
随机试题
[originaltext]W:Tellme,Peter.WhatmakesHaroldssofamous?M:Well,it’sth
Whatarethemanandthewomantalkingabout?[originaltext]M:I’vejustbeenr
[originaltext]M:Weplantogotothebeachafterclass.Wanttocome?W:I’dl
根据《劳动合同法》的规定,下列哪种情形下用人单位不可以解除劳动合同:A.在试用期
当从业人员发现直接危及人身安全的紧急情况时,有权停止作业或在采取可能的应急措施后
根据控制论创始人维纳及信息论的奠基者香农对信息的定义,信息是()A.一种物质
下列三维标志中,可以作为商标注册的是( )。A.仅仅是由于商品自身性质产生的形
能够从上述资料中推出的是: A.2008年上饶市初中和高中学校数在全
为了加强质量把关,必须在一些质量控制的()设置检验站。 A.薄弱环节B.关
实施清创术的最佳时机应该是 A.伤后2小时内进行 B.伤后4小时内进行 C
最新回复
(
0
)