托福阅读TPO18(试题+答案+译文)第3篇:Lightning

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托福阅读原文

【1】Lightning is a brilliant flash of light produced by an electrical discharge from a storm cloud. The electrical discharge takes place when the attractive tension between a region of negatively charged particles and a region of positively charged particles becomes so great that the charged particles suddenly rush together. The coming together of the oppositely charged particles neutralizes the electrical tension and releases a tremendous amount of energy, which we see as lightning. The separation of positively and negatively charged particles takes place during the development of the storm cloud.

【2】The separation of charged particles that forms in a storm cloud has a sandwich-like structure. Concentrations of positively charged particles develop at the top and bottom of the cloud, but the middle region becomes negatively charged. Recent measurements made in the field together with laboratory simulations offer a promising explanation of how this structure of charged particles forms. What happens is that small (millimeter-to centimeter-size) pellets of ice form in the cold upper regions of the cloud. When these ice pellets fall, some of them strike much smaller ice crystals in the center of the cloud. The temperature at the center of the cloud is about -15℃ or lower. At such temperatures, the collision between the ice pellets and the ice crystals causes electrical charges to shift so that the ice pellets acquire a negative charge and the ice crystals become positively charged. Then updraft wind currents carry the light, positively charged ice crystals up to the top of the cloud. The heavier negatively charged ice pellets are left to concentrate in the center. This process explains why the top of the cloud becomes positively charged, while the center becomes negatively charged. The negatively charged region is large: several hundred meters thick and several kilometers in diameter. Below this large, cold, negatively charged region, the cloud is warmer than -15℃, and at these temperatures, collisions between ice crystals and falling ice pellets produce positively charged ice pellets that then populate a small region at the base of the cloud.

【3】Most lightning takes place within a cloud when the charge separation within the cloud collapses. However, as the storm cloud develops, the ground beneath the cloud becomes positively charged and lightning can take place in the form of an electrical discharge between the negative charge of the cloud and the positively charged ground. Lightning that strikes the ground is the most likely to be destructive, so even though it represents only 20 percent of all lightning, it has received a lot of scientific attention.

【4】Using high-speed photography, scientists have determined that there are two steps to the occurrence of lightning from a cloud to the ground. First, a channel, or path, is formed that connects the cloud and the ground. Then a strong current of electrons follows that path from the cloud to the ground, and it is that current that illuminates the channel as the lightning we see.

【5】The formation of the channel is initiated when electrons surge from the cloud base toward the ground. When a stream of these negatively charged electrons comes within 100 meters of the ground it is met by a stream of positively charged particles that comes up from the ground. When the negatively and positively charged streams meet, a complete channel connecting the cloud and the ground is formed. The channel is only a few centimeters in diameter, but that is wide enough for electrons to follow the channel to the ground in the visible form of a flash of lightning. The stream of positive particles that meets the surge of electrons from the cloud often arises from a tall pointed structure such as a metal flagpole or a tower. That is why the subsequent lightning that follows the completed channel often strikes a tall structure.

【6】Once a channel has been formed, it is usually used by several lightning discharges, each of them consisting of a stream of electrons from the cloud meeting a stream of positive particles along the established path. Sometimes, however, a stream of electrons following an established channel is met by a positive stream making a new path up from the ground. The result is a forked lightning that strikes the ground in two places.

托福阅读试题

1.According to paragraph 1, all of the following take place in the development of a flash of lightening EXCEPT

A.great tension between two oppositely charged regions.

B.an increase in negatively charged particles over positively charged particles.

C.oppositely charged particles coming together.

D.the release of electrical energy in the form of visible light.

2.The word “tremendous” in passage 1 is closest in meaning to

A.distinct.

B.growing.

C.huge.

D.immediate.

3.According to paragraph 2, what causes ice crystal to become positively charged?

A.Collisions with ice pellets.

B.Collisions with negatively charged ice crystals at the base of the cloud.

C.Becoming concentrated in the central region of the cloud.

D.Forming at a temperature greater than -15℃.

4.The word “acquire” in passage 2 is closest in meaning to

A.reject.

B.obtain.

C.need.

D.produce.

5.According to paragraph 2, why are positively charged ice pellets produced in the lower part of the cloud?

A.Collisions between ice crystals and ice pellets increase in number in the lower part of the cloud.

B.The lower part of the cloud is smaller than the region above it.

C.More ice pellets than ice crystals reach the lower part of the cloud.

D.Temperature in the lower part of the cloud are warmer than -15℃.

6.According to paragraph 2, the middle region of a cloud becomes negatively charged due to all of the following EXCEPT

A.a shift of electrical charged between ice pellets and ice crystals.

B.negatively charged ice pellets that remain in the middle.

C.a temperature of -15℃ or less.

D.the development of a positive charge at the base of the cloud.

7.It can be inferred from paragraph 2 that part of the reason that the top of a storm cloud becomes positively charged is that

A.the top of the cloud is warmer than the middle of the cloud.

B.the middle of the cloud is already occupied by positively charged particles.

C.the negatively charged ice pellets are too heavy to be carried by the updrafts that move ice crystals.

D.collisions between ice pellets in the top of the cloud produce mainly positively charged particles.

8.The author remarks that (in paragraph 3)“Lightning that strikes the ground is the most likely to be destructive” in order to explain why

A.this form of lightning has been investigated so much.

B.this form of lightning is not as common as lightning within a cloud.

C.scientific understanding of this form of lightning is important.

D.the buildup of positive charge on the ground beneath a storm cloud can have serious consequences.

9.The word “illuminates” in passage 4 is closet in meaning to

A.opens.

B.completes.

C.lights.

D.electrifies.

10.According to paragraph5, which of the following is true of the stream of charged particles from the ground?

A.It prevents streams of electrons from the cloud from striking the ground.

B.It completes a channel that connects the storm cloud with the ground.

C.It produces a stream of electrons from the cloud.

D.It widens the path made by the initial stream of electrons from the cloud.

11.Which of the following claims about lightning strikes can be inferred from paragraph 5?

A.During a lightning strike the diameter of the channel the electrons follow is considerably enlarged beyond a few centimeters.

B.A building is unlikely to be hit by lightning unless it is at least 100 meters tall.

C.A building is hit by a lightning strike because the building itself has first determined the path the lightening then takes to it.

D.The light of a lightning strike first appears at the point where the streams of negative and positive particles meet.

12.The word “initiated”in paragraph 5 is closet in meaning to

A.started.

B.intensified.

C.finished.

D.expected.

13. Look at the four squares [■] that indicate where the following sentence could be added to the passage. Where would the sentence best fit? The descending stream of electrons divides at the point where the new positive-stream channel intersects the established path.

The formation of the channel is initiated when electrons surge from the cloud base toward the ground. When a stream of these negatively charged electrons comes within 100 meters of the ground it is met by a stream of positively charged particles that comes up from the ground. When the negatively and positively charged streams meet, a complete channel connecting the cloud and the ground is formed. The channel is only a few centimeters in diameter, but that is wide enough for electrons to follow the channel to the ground in the visible form of a flash of lightning. The stream of positive particles that meets the surge of electrons from the cloud often arises from a tall pointed structure such as a metal flagpole or a tower. That is why the subsequent lightning that follows the completed channel often strikes a tall structure. ■【A】

Once a channel has been formed, it is usually used by several lightning discharges, each of them consisting of a stream of electrons from the cloud meeting a stream of positive particles along the established path. ■【B】 Sometimes, however, a stream of electrons following an established channel is met by a positive stream making a new path up from the ground. ■【C】 The result is a forked lightning that strikes the ground in two places. ■【D】

14. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THERR answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.

Lightning takes place when a separation of a positive and negative electrical particles that develops in a storm could suddenly collapses.

A.A storm cloud first develops a positively charged layer at the top, then a negatively charged middle layer, and finally, a positively charged layer at the bottom.

B.A separation of oppositely charged particles in clouds develops from collisions of falling ice pellets with ice crystals, from updrafts, and from temperature variations.

C.Lightning from cloud to ground follows a channel that forms when a stream of electrons moving down meets a stream of positive particles coming up from the ground.

D.Field studies, laboratory simulations, and high-speed photography have all been used to investigate the way charge separations develop in clouds.

E.Lightning from a cloud to the ground is more likely to be destructive than is lightning that takes place within a cloud.

F.Once a channel has been formed, it is usually used by several successive electrical discharges that illuminate the channel as flashes of lightning.

托福阅读答案

1.EXCEPT题，排除法，A的tension和做关键词定位至第二句，正确，不选;B的negatively和positively charged particles同样定位至第二句，但原文没有比较，所以B没说，选;C的come together和D的release做关键词定位都至倒数第二句，都正确，都不选。

2.tremendous大量的，巨大的，所以正确答案是huge。原句说当带相反电荷的例子碰到一起的时候发生中和并释放什么样的能量，就是我们能看到的闪电，大家都知道闪电的能量很大，所以选huge，C。A不同B增大D立刻都不靠谱。

3.以ice crystal和positively charged做关键词定位至第七句，说在这样的温度下，ice pellet和ice crystal的碰撞转移了电荷，使得pellet带负电，crystal带正电，所以答案应该是A碰撞;B虽然也说到碰撞，但不是和负电碰撞;D的温度不是带正电的决定条件。

4.acquire获得，所以答案obtain正确，正如上题，原句说ice pellet和ice crystal的碰撞转移了电荷，使得pellet怎么样负电，crystal带正电，至少猜出acquire应该和become差不多，是个从无到有的过程，答案是B。需要不一定有，C错;A拒绝与原文相反;D错，电荷不能产生。

5.以positively charged ice pellets做关键词定位至最后一句，说在这个很大的，带负电的区域之下，碰撞 产生了positively charged pellets，所以答案是D。A的increase in number，B的smaller和C的比较原文都没说。

6.EXCEPT题，排除法，A的ice pellets and ice crystals做关键词定位至第七句，正确，不选;B的in the middle做关键词定位至倒数第四句，正确，不选;C的数字做关键词定位至第六句，正确，不选;D的the base of the cloud做关键词定位都至最后一句，但倒数第三句已经说过this process explains，也就是说原因到倒数第三句就给完了，D不是原因，错，选。

7.修辞目的题，修辞点所在句子说这种闪电具有破坏性，所以尽管这类闪电只占全部的20%，它仍然受到了很多关注，也就是解释下受关注是因为具有破坏性，所以答案是A。

8.illuminate发光，照射，所以C的light是正确答案。原句说一股强烈的电子流沿通路从云层到地面，并且怎么样了那个通路，成为我们所看到的闪电，如果不照亮怎么看到闪电呢?所以C正确;A打开B完成D使带电都不能解释看见，所以都不对。

9.以stream of charged particles from the ground做关键词定位至第二句，说来自地面的带负电的电子流会在地面以上100米左右碰上来自云层的带正电的电子流，然后又说当二者碰在一起的时候就形成了通路，所以B形成通路是正确的。A的prevent，C的produce和D的widen原文都没说。

10.因此题关键词比较难找，所以用排除法。A的diameter of the channel和centimeter做关键词定位至第四句，但原文没有信息能推出widen，所以A错;B的数字做关键词定位至第二句，说100米内正负电荷就会碰到，所以B说反;C的path做关键词定位至最后一句的channel，说正电荷通常升起自地面上的一个高点，比如旗杆，然后闪电由通路到达地面，也就是说旗杆等高的建筑物是这个channel的一部分，所以C说building决定了path是对的，选C;D的first appear原文没有相关信息。

11.以top of the storm cloud做关键词定位至倒数第五句，说向上的气流将轻的，带正电的粒子带到云层上部，这自然是上部云层带正电的原因，反过来说也就是带负电的粒子很重，所以没有上来，所以答案是C。原文只是说了中部和下部的温度，上部温度没有信息，所以A错;由倒数第四句可知中部是负电，B说反了;D原文也没说。

12.initiate开始，所以正确答案是A。原文说通路形成怎么了，当云层底部的电子向地面运动的时候，接着又说这些云层中的粒子和地面上来的粒子碰到一起之后，闪电的通路就完全形成了，也就是上文的云层底部的电子下来是形成的开始，所以答案是start，C结束说反了;B加强和D期望完全不靠谱。

13.两个过渡点，名词established path和动词divide，根据established path可以确定答案是A/B/C，注意原文中established channel和established path是同义词，所以不要忘了C答案，根据divide与最后一句forked的同义替换确定C或者D，所以C是答案。

14.A storm选项明显不对，因为正负电荷是同时形成的，没有先后，A不选。Lightning from cloud to ground选项对应原文第五段的第一句和第三句，C正确。Lightning from a cloud to the ground选项MS对应第三段最后一句，但原文没有比较，E不选。A separation选项对应原文第二段，B正确。Field选项是原文第二段和第四段的细节，D不选。Once选项对应原文最后一段第一句，F正确。

托福阅读译文

【1】闪电是由雷雨云放电产生的一道明亮夺目的闪光。当带正电荷粒子区域与带负电荷粒子区域之间的吸引力大到使带电粒子瞬间碰撞到一起就会发生放电现象。相反的带电粒子的结合中和了电压并释放出巨大的能量，这就是我们看到的闪电。在雷雨云形成的过程中正负带电粒子相互分离。

【2】形成雷雨云的带电粒子的分离具有一种三明治结构。带正电的粒子聚集在云的顶部和底部，但是中间区域形成的是带负电的粒子。近期的野外测量以及实验室模拟为这种带电粒子的排列结构提供了可能的解释。实际上在此过程中在云层较冷的上部区域形成了细小的(毫米到厘米大小)冰丸。当这些冰丸飘落时，一部分会与云层中心比冰丸小得多的冰晶相撞。云层中心的温度大约在零下15摄氏度或者更低。在此温度下，冰丸和冰晶的撞击会使电荷发生转移，冰丸由此获得了负电而冰晶获得了正电。随后上升气流会将较轻的正电冰晶带到云的顶部。较重的负电冰丸会留在云层中部并积累起来。这个过程解释了为什么云的顶部带正电而中部带负电。带负电的区域非常大：厚度达数百米，直径达几千米。位于这片又大又冷的带负电区域之下的云层的温度要高于零下15摄氏度，在此温度下，冰晶和降落的冰丸的碰撞会产生带正电荷的冰丸，于是在云层的底部聚集成一小片区域。

【3】大部分的闪电发生在云层塌陷电荷分离的云层内部。但是，随着雷雨云的发展，云层下方的地面会带上正电，闪电就能够在带负电的云和带正电的陆地之间以放电的形式发生。击中地面的闪电是最有可能带有破坏性的，所以即使它只占所有闪电的20%，还是受到了很大的科学关注。

【4】通过高速摄影，科学家已经确定从云层到地面发生闪电的过程有两步。首先，要建立连接云层和地面的通道或者路径。然后强电流会沿着这条通道从云层传向地面，这股照亮通道的电流就是我们看到的闪电。

【5】电子从云层基部涌向地面就会开始形成通道。当这些负电荷距离地面不到100米的时候，会遇到来自地面的带正电的粒子流。一旦正负带电粒子流相遇，一条连接云层和地面的完整的通道便形成了。这个通道直径仅有几厘米，但是已经足以使电子以一道闪电这种可见的形式通过通道到达地面。那些与从云层涌来的电子相遇的带正电的粒子流通常来自于高大的带尖顶的建筑物，例如金属旗杆或塔。这就是为什么接下来通过完整通道的闪电往往会击中高层建筑的原因。

【6】一旦通道形成，同一条通道可以发生多次闪电放电，每一次都是来自云层的电子流在已有通道上遇到带正电的粒子。但是有时候，通过已有通道的电子流会遇到从地面新路径来的带正电的电子流。结果就是形成在两处击中地面的叉状闪电。

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