每日一练：职称英语考试理工类每日一练(2015-12-21)
【单选题】
Invisibility Ring
Scientists can't yet make aninvisibility cloak1 like the one that Harry Potter2 uses.But,for the firsttime,they've constructed a simple cloaking device that makes itself andsomethingplaced inside it invisible to microwaves.
When a person"sees"anobject,his or her eye senses many different waves of visiblelight as theybounce off the object.The eye and brain then work together to organizethesesensations and reconstruct the object's original shape.So,to make anobject invisible,scientists have to keep waves from bouncing off it.And theyhave to make sure the objectcasts no shadow.Otherwise,the absence of reflectedlight on one side would give the obiectaway.
Invisibility isn't possible yetwith waves of light that the human eye can see.But it is nowpossible withmicrowaves.Like visible light,microwaves are a form of radiant energy.Theyarepart of the electromagnetic spectrum,which also includes radio waves,infraredlight,ultraviolet rays,X rays,and gamma rays.The wavelengths of microwaves areshorter thanthose of radio waves but longer than those of visible light.
Thescientists'new"invisibility device"is the size of a drink coaster andshaped like aring.The ring is made of a special material with unusualability.When microwaves strike thering,very few bounce off it.Instead,they passthrough the ring,which bends the waves allthe way around until they reach theopposite side.The waves then return to their originalpaths.
To a detector set up to receivemicrowaves on the other side of the ring,it looks as if thewaves never changedtheir paths as if there were no object in the way! So,the ring is effectivelyinvisible.
When the researchers put asmall cdpper loop inside the ring,it,too,is nearly invisible.However,thecloaking device and anything inside it do cast a pale shadow.And thedeviceworks only for microwaves,not for visible light or any kind ofelectromagnetic radiation.So,Harry Potter's invisibility cloak doesn't have anyreal competition yet.
练习：
1.Harry Potter is mentioned inthe passage,because scientists
A.can now make an invisiblecloak of the same kind as he uses.
B.try to make an invisiblecloak of the same kind as he uses.
C.try to invent a deviceSimilar in idea to the invisible cloak he uses.
D.know that it is possible tomake an invisible cloak of the same kind.
2.What is true of microwaves?
A.Their wavelengths are shorterthan those of visible light.
B.Their wavelengths are longerthan those of visible light.
C.They are different fromvisible light as they are a kind of radiant energy.
D.They are visible to the humaneye.
3.What is NOT true of theinvisibility device?
A.It is made of a specialmaterial with unusual ability.
B.Microwaves bounce off it whenthey strike it.
C.Microwaves pass through itwhen they strike it.
D.It bends the microwaves allthe way around until they reach the opposite side.
4.What does theword"coaster"mean in the passage?
A.A disk or plate placed undera drinking glass to protect a table top.
B.A vessel engaged in coastaltrade.
C.A roller coaster.
D.A resident of a coastal area.
5.Harry Potter's invisibilitycloak doesn't have any real competition yet, because .
A.scientists have not found outhow his cloak works.
B.the cloaking device is a totalfailure.
C.the cloaking device worksonly for microwaves.
D.the cloaking deviceworks only for visible light在下面提交答题后即可查看答案与考友试题分析
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