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.
Paragraph1 : 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.
1. According to paragraph 1, all of the following take place in the development of a flash of lightening EXCEPT
○ great tension between two oppositely charged regions
○ an increase in negatively charged particles over positively charged particles
○ oppositely charged particles coming together
○ the release of electrical energy in the form of visible light
2.The word “tremendous” in the passage is closest in meaning to
○ distinct
○ growing
○ huge
○ immediate
Paragraph 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.According to paragraph2, what causes ice crystal to become positively charged?
○ Collisions with ice pellets
○ Collisions with negatively charged ice crystals at the base of the cloud
○ Becoming concentrated in the central region of the cloud
○ Forming at a temperature greater than -15℃
4.The word “acquire” in the passage is closest in meaning to
○ reject
○ obtain
○ need
○ produce
5. According to paragraph2, why are positively charged ice pellets produced in the lower part of the cloud?
○ Collisions between ice crystals and ice pellets increase in number in the lower part of the cloud.
○ The lower part of the cloud is smaller than the region above it.
○ More ice pellets than ice crystals reach the lower part of the cloud.
○ Temperature in the lower part of the cloud are warmer than -15℃.
6.According to paragraph2, the middle region of a cloud becomes negatively charged due to all of the following EXCEPT
○ a shift of electrical charged between ice pellets and ice crystals
○ negatively charged ice pellets that remain in the middle
○ a temperature of -15℃ or less
○ 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
○ the top of the cloud is warmer than the middle of the cloud
○ the middle of the cloud is already occupied by positively charged particles
○ the negatively charged ice pellets are too heavy to be carried by the updrafts that move ice crystals
○ collisions between ice pellets in the top of the cloud produce mainly positively charged particles
Paragraph 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.
8.The author remarks that “Lightning that strikes the ground is the most likely to be destructive” in order to explain why
○ this form of lightning has been investigated so much
○ this form of lightning is not as common as lightning within a cloud
○ scientific understanding of this form of lightning is important
○ the buildup of positive charge on the ground beneath a storm cloud can have serious consequences
Paragraph 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.
9.The word “illuminates” in the passage is closet in meaning to
○ opens
○ completes
○ lights
○ electrifies
Paragraph 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.
10. According to paragraph5, which of the following is true of the stream of charged particles from the ground?
○ It prevents streams of electrons from the cloud from striking the ground.
○ It completes a channel that connects the storm cloud with the ground.
○ It produces a stream of electrons from the cloud.
○ 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?
○ During a lightning strike the diameter of the channel the electrons follow is considerably enlarged beyond a few centimeters.
○ A building is unlikely to be hit by lightning unless it is at least 100 meters tall.
○ A building is hit by a lightning strike because the building itself has first determined the path the lightening then takes to it.
○ The light of a lightning strike first appears at the point where the streams of negative and positive particles meet.
12.The word “initiated” is closet in meaning to
○ started
○ intensified
○ finished
○ expected
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. ■
13.Look at the four squares [■] that indicate where the following sentence could be added to the passage.
The descending stream of electrons divides at the point where the new positive-stream channel intersects the established path.
Where would the sentence best fit?
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.
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○ 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.
○ A separation of oppositely charged particles in clouds develops from collisions of falling ice pellets with ice crystals, from updrafts, and from temperature variations.
○ 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.
○ Field studies, laboratory simulations, and high-speed photography have all been used to investigate the way charge separations develop in clouds.
○ Lightning from a cloud to the ground is more likely to be destructive than is lightning that takes place within a cloud.
○ Once a channel has been formed, it is usually used by several successive electrical discharges that illuminate the channel as flashes of lightning.
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參考答案：
1． 2
2． 3
3． 1
4． 2
5． 4
6． 4
7． 3
8． 1
9． 3
10． 2
11． 3
12． 1
13． 3
14． A separation of …
Lightning from cloud to ground …
Once a channel has …
閃電是由雷雨云放電產(chǎn)生的一道明亮奪目的閃光。當(dāng)帶正電荷粒子區(qū)域與帶負(fù)電荷粒子區(qū)域之間的吸引力大到使帶電粒子瞬間碰撞到一起就會發(fā)生放電現(xiàn)象。相反的帶電粒子的結(jié)合中和了電壓并釋放出巨大的能量，這就是我們看到的閃電。在雷雨云形成的過程中正負(fù)帶電粒子相互分離。
形成雷雨云的帶電粒子的分離具有一種三明治結(jié)構(gòu)。帶正電的粒子聚集在云的頂部和底部，但是中間區(qū)域形成的是帶負(fù)電的粒子。近期的野外測量以及實驗室模擬為這種帶電粒子的排列結(jié)構(gòu)提供了可能的解釋。實際上在此過程中在云層較冷的上部區(qū)域形成了細(xì)小的（毫米到厘米大小）冰丸。當(dāng)這些冰丸飄落時，一部分會與云層中心比冰丸小得多的冰晶相撞。云層中心的溫度大約在零下15攝氏度或者更低。在此溫度下，冰丸和冰晶的撞擊會使電荷發(fā)生轉(zhuǎn)移，冰丸由此獲得了負(fù)電而冰晶獲得了正電。隨后上升氣流會將較輕的正電冰晶帶到云的頂部。較重的負(fù)電冰丸會留在云層中部并積累起來。這個過程解釋了為什么云的頂部帶正電而中部帶負(fù)電。帶負(fù)電的區(qū)域非常大：厚度達(dá)數(shù)百米，直徑達(dá)幾千米。位于這片又大又冷的帶負(fù)電區(qū)域之下的云層的溫度要高于零下15攝氏度，在此溫度下，冰晶和降落的冰丸的碰撞會產(chǎn)生帶正電荷的冰丸，于是在云層的底部聚集成一小片區(qū)域。
大部分的閃電發(fā)生在云層塌陷電荷分離的云層內(nèi)部。但是，隨著雷雨云的發(fā)展，云層下方的地面會帶上正電，閃電就能夠在帶負(fù)電的云和帶正電的陸地之間以放電的形式發(fā)生。擊中地面的閃電是最有可能帶有破壞性的，所以即使它只占所有閃電的20%，還是受到了很大的科學(xué)關(guān)注。
通過高速攝影，科學(xué)家已經(jīng)確定從云層到地面發(fā)生閃電的過程有兩步。首先，要建立連接云層和地面的通道或者路徑。然后強(qiáng)電流會沿著這條通道從云層傳向地面，這股照亮通道的電流就是我們看到的閃電。
電子從云層基部涌向地面就會開始形成通道。當(dāng)這些負(fù)電荷距離地面不到100米的時候，會遇到來自地面的帶正電的粒子流。一旦正負(fù)帶電粒子流相遇，一條連接云層和地面的完整的通道便形成了。這個通道直徑僅有幾厘米，但是已經(jīng)足以使電子以一道閃電這種可見的形式通過通道到達(dá)地面。那些與從云層涌來的電子相遇的帶正電的粒子流通常來自于高大的帶尖頂?shù)慕ㄖ�，例如金屬旗桿或塔。這就是為什么接下來通過完整通道的閃電往往會擊中高層建筑的原因。
一旦通道形成，同一條通道可以發(fā)生多次閃電放電，每一次都是來自云層的電子流在已有通道上遇到帶正電的粒子。但是有時候，通過已有通道的電子流會遇到從地面新路徑來的帶正電的電子流。結(jié)果就是形成在兩處擊中地面的叉狀閃電。
