Official18 托福阅读Passage3 Lighting文本+题目原文+答案解析【雷哥托福】2019-01-30 17:32:38 发布 来源：雷哥托福
TPO18 托福阅读Passage3 Lighting文本+题目原文+答案解析
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.
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.
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.
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.
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.█
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.█
TPO18托福阅读Passage3 Lighting 题目
Question 1 of 14: According to paragraph 1, all of the following take place in the development of a flash of lightning 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
Question 2 of 14: The word “tremendous” in the passage is closest in meaning to
Question 3 of 14: According to paragraph 2, what causes ice crystals 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℃
Question 4 of 14: The word “acquire” in the passage is closest in meaning to
Question 5 of 14: 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. Temperatures in the lower part of the cloud are warmer than -15°C.
Question 6 of 14: 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 charges 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
Question 7 of 14: The author remarks that “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
Question 8 of 14: The word “illuminates” in the passage is closest in meaning to
Question 9 of 14: According to paragraph 5, 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
Question 10 of 14: 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 lightning 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
Question 11 of 14: 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
Question 12 of 14: The word “initiated” is closest in meaning to
Question 13 of 14: 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.
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.
Question 14 of 14: Lightning takes place when a separation of positive and negative electrical particles that develop in a storm cloud 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. 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
C. Lightning from a cloud to the ground is more likely to be destructive than is lightning that takes place within a cloud
D. A separation of oppositely charged particles in clouds develops from collisions of falling ice pellets with ice crystals, from updrafts and from temperature variations
E. Field studies laboratory simulations and high-speed photography have all been used to investigate the way charge separations develop in clouds
F. Once a channel has been formed it is usually used by several successive electrical discharges that illuminate the channel as flashes of lightning
Question 1 of 14
解析：EXCEPT题，可以用排除法做，A的tension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，但原文没有比较谁多谁少，所以B未提及，可选；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。
Question 2 of 14
Question 3 of 14
解析：以ice crystal和positively charged做关键词定位至第二段第七句，提到在这样的温度下，ice pellet和ice crystal的碰撞转移了电荷，使得ice pellet带负电，ice crystal带正电，所以答案应该是A；B虽然也说到碰撞，但不是和负电ice crystals碰撞；C的concentrate in the center为关键词定位到第九句，说的是带负电的ice pellets，信息错误，且与问题无关；D与原文相反，原文说的是-15°C以下发生的碰撞。
Question 4 of 14
Question 5 of 14
解析：以positively charged ice pellets做关键词定位至最后一句，提到：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，ice crystals和降落的ice pellets的碰撞会产生带positively charged ice pellets，于是在云层的底部聚集成一小片区域。对应D选项。这样的温度是带正电的ice pellets产生在云底部的原因。
Question 6 of 14
解析：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完整了，D不是原因，错误，可选。
Question 7 of 14
Question 8 of 14
Question 9 of 14
解析：以stream of charged particles from the ground做关键词定位至第五段第二句，提到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原文都未提及。
Question 10 of 14
解析：因此题关键词比较难找，所以用排除法做。A的diameter of the channel和centimeter做关键词定位至第五段第四句，但原文没有信息能推出widen，所以A错误；B的数字做关键词定位至第二句，提到100米内正负电荷就会碰到，所以B与原文相反；C的path做关键词定位至最后一句的channel，提到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，所以C说building决定了path是正确的；D的first appear原文没有相关信息。
Question 11 of 14
解析：以top of the storm cloud做关键词定位至倒数第五句，提到向上的气流将轻的、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。原文只是提到了中部和下部的温度，上部温度没有信息，所以A错误；由倒数第四句可知中部是负电，B和原文相反；D原文也未提及。
Question 12 of 14
Question 13 of 14
解析：插入句没有逻辑提示词或代词，因此只能从意义上理解。这一句说的是：当新的正电子通道与已建立好的通道相遇时，上升的电子流就会分开。而C前面刚好说到a new path。并且意义上也正确，插入句说到上升的电子流会分开，后面接的就是分开的结果：分叉闪电会击中不同的两块地面。
Question 14 of 14