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visibility Ring
Scientists can’t yet make an invisibility cloak1 like the one that Harry Potter2 uses.But，for the first time，they’ve constructed a simple cloaking device that makes itself and somethingplaced inside it invisible to microwaves.
When a person “sees” an object，his or her eye senses many different waves of visiblelight as they bounce off the object.The eye and brain then work together to organize thesesensations and reconstruct the object’s original shape. So，to make an object invisible，scientists have to keep waves from bouncing off it.And they have to make sure the objectcasts no shadow.Otherwise，the absence of reflected light on one side would give the obiectaway.
Invisibility isn’t possible yet with waves of light that the human eye can see.But it is nowpossible with microwaves.Like visible light，microwaves are a form of radiant energy.Theyare part of the electromagnetic spectrum，which also includes radio waves，infrared light，ultraviolet rays，X rays，and gamma rays.The wavelengths of microwaves are shorter thanthose of radio waves but longer than those of visible light.
The scientists’ new “invisibility device” is the size of a drink coaster and shaped like aring.The ring is made of a special material with unusual ability.When microwaves strike thering，very few bounce off it.Instead，they pass through the ring，which bends the waves allthe way around until they reach the opposite side.The waves then return to their originalpaths.
To a detector set up to receive microwaves on the other side of the ring，it looks as if thewaves never changed their paths as if there were no object in the way! So，the ring is effectively invisible.
When the researchers put a small cdpper loop inside the ring，it，too，is nearly invisible. However，the cloaking device and anything inside it do cast a pale shadow.And the deviceworks only for microwaves，not for visible light or any kind of electromagnetic radiation.So，Harry Potter’s invisibility cloak doesn’t have any real competition yet.
词汇：
invisibility/invizE5biliti/n.看不见，无形 spectrum/5spektrEm/n.光谱
cloak/klEuk/斗篷，披风 infrared/5infrE5red/adj.红外线的
microwave/5maikrEuweiv/n.微波 ultraviolet ray 紫外线
reconstruct/5ri:kEn5strQkt/v.重建 gamma ray 伽马射线
radiant/5reidjEnt/adj.辐射的 wavelength/5weivleNW/n.波长
electromagnetic/IlektrEJ5mA^nItIk/adj.电磁的coaster/5kEustE(r)/n.托盘，垫子
练习：
1.Harry Potter is mentioned in the passage，because scientists
Acan now make an invisible cloak of the same kind as he uses.
Btry to make an invisible cloak of the same kind as he uses.
Ctry to invent a device Similar in idea to the invisible cloak he uses.
Dknow that it is possible to make an invisible cloak of the same kind.
2.What is true of microwaves?
ATheir wavelengths are shorter than those of visible light.
BTheir wavelengths are longer than those of visible light.
CThey are different from visible light as they are a kind of radiant energy.
DThey are visible to the human eye.
3.What is NOT true of the invisibility device?
AIt is made of a special material with unusual ability.
BMicrowaves bounce off it when they strike it.
CMicrowaves pass through it when they strike it.
DIt bends the microwaves all the way around until they reach the opposite side.
4.What does the word “coaster” mean in the passage?
AA disk or plate placed under a drinking glass to protect a table top.
BA vessel engaged in coastal trade.
CA