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
93
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
Labelthediagrambelow.ChooseNOMORETHANONEWORDAND/ORANUMBERfromthepassageforeachanswer.Writeyouranswersinbo
InsidethemindoftheconsumerCouldbrain-scanningtechnologyprovideanaccuratewaytoassesstheappealof
InsidethemindoftheconsumerCouldbrain-scanningtechnologyprovideanaccuratewaytoassesstheappealof
【21】Whichbeareatsplants?
Theuniversityhasproduceda______toinformstudentsaboutthedifferentaccommodationoptionsavailable.Thisisthebesta
Completethenotesbelow.UseNOMORETHANTHREEWORDSORANUMBERforeachanswer.INTERNATIONALDRIVINGLICENSESFACTS
STUDENTBANKINGNote:Maynotbeallowedallfacilitiesgiventoresidentstudents.FundingMustprovide【T14】______.Icans
WhatactionsdoBradandHelenagreetodoregardingthefollowingpreparationtasks?ChooseFOURanswersfromtheboxandwrite
AsystemwasdevelopedtocontroltrafficcongestionontheM25motorway.Expertsuse【L5】________informationfromthemotorw
随机试题
2011年韩玉笙因盖房挖地基,发现一个瓦罐,内有500块银元及一块棉布,上面写着“为防日寇,特埋此。王天民,1938年7月5日”。王天民为王大水的爷爷,1938年7月8日被日寇杀害。该500块银元()
A.热证B.表证C.实证D.虚证E.寒证怔忡,临床上多见于
A.肉桂B.杜仲C.白鲜皮D.秦皮E.厚朴内表面红棕色而油润,两层中间有1条黄棕色的线纹,气香浓烈,味甜、辣的药材是()。
A.花椒B.藏红花C.细辛D.泽泻E.牡丹皮采用对抗贮存法养护中药时可与蛤蚧同贮的是()。
本单位内部经办经济业务的部门或人员在办理经济业务时所填制的凭证称为()。(4.2)
问题解决的基本特点是什么?
Wehaveallheardhowtimeismorevaluablethanmoney,butisit【C1】________tohavetoomuch?I【C2】________backinhighschool
认为人的发展主要依靠外在的力量,诸如环境的刺激和要求、他人的影响和学校的教育等,持这种观点的教育家是()。
Inits14yearsof______,theEuropeanUnionhasearnedthescornofitscitizensandskepticismfromtheUnitedStates.
Walking—likeswimming,bicyclingandrunning—isanaerobicexercise,【C1】_________buildsthecapacityforenergyoutputandphys
最新回复
(
0
)