YÖKDİL Fen Okuma Paragrafı Soruları

Question 1

Engineers have long known that a metal component can break under a load far smaller than the one it was designed to carry. The cause is usually fatigue, a gradual form of damage produced not by a single heavy force but by many repetitions of a modest one. Each time a part is bent, stretched or twisted and then released, microscopic changes accumulate in its structure. Eventually, a tiny crack appears, most often at a point where stress is concentrated, such as a sharp corner, a hole drilled for a bolt or a scratch left during manufacture. With every further cycle of loading, the crack grows a little longer, while the part continues to perform its function normally. Because the remaining sound metal still carries the load, there may be no visible sign that anything is wrong. Only when the crack has reduced the cross-section so much that the rest of the material can no longer bear the load does the component snap, often suddenly. This hidden progression explains why fatigue has been responsible for many unexpected failures in railway axles, aircraft and bridges. Designers now try to reduce the risk in several ways. They avoid sharp changes in shape, smooth the surfaces of critical parts and estimate how many cycles a component will experience during its working life. In addition, parts that cannot be allowed to fail are inspected at regular intervals with methods, such as ultrasound, that can reveal cracks hidden beneath the surface. The aim is not to prevent every crack from forming, but to find any crack and replace the part long before it becomes dangerous.

What is the passage mainly about?

Accepted Answer

How repeated modest loads gradually weaken metal parts and how engineers manage this risk

Answer

How ultrasound inspections have made it possible to predict the working life of metal parts

Answer

Why metal parts that carry heavy loads crack more often than those that carry light ones

Answer

How manufacturing flaws such as scratches cause railway axles and bridges to fail

Answer

Why engineers now try to design metal components that are completely free of cracks

Question 2

Engineers have long known that a metal component can break under a load far smaller than the one it was designed to carry. The cause is usually fatigue, a gradual form of damage produced not by a single heavy force but by many repetitions of a modest one. Each time a part is bent, stretched or twisted and then released, microscopic changes accumulate in its structure. Eventually, a tiny crack appears, most often at a point where stress is concentrated, such as a sharp corner, a hole drilled for a bolt or a scratch left during manufacture. With every further cycle of loading, the crack grows a little longer, while the part continues to perform its function normally. Because the remaining sound metal still carries the load, there may be no visible sign that anything is wrong. Only when the crack has reduced the cross-section so much that the rest of the material can no longer bear the load does the component snap, often suddenly. This hidden progression explains why fatigue has been responsible for many unexpected failures in railway axles, aircraft and bridges. Designers now try to reduce the risk in several ways. They avoid sharp changes in shape, smooth the surfaces of critical parts and estimate how many cycles a component will experience during its working life. In addition, parts that cannot be allowed to fail are inspected at regular intervals with methods, such as ultrasound, that can reveal cracks hidden beneath the surface. The aim is not to prevent every crack from forming, but to find any crack and replace the part long before it becomes dangerous.

According to the passage, a fatigue crack usually begins ----.

Accepted Answer

at points where corners, holes or scratches make stress build up

Answer

in the thickest section of the part, where the load is carried most heavily

Answer

beneath the surface, in areas that cannot be reached by ultrasound

Answer

after a single load greater than the one the part was designed to carry

Answer

only once the part has already begun to bend visibly under its load

Question 3

Engineers have long known that a metal component can break under a load far smaller than the one it was designed to carry. The cause is usually fatigue, a gradual form of damage produced not by a single heavy force but by many repetitions of a modest one. Each time a part is bent, stretched or twisted and then released, microscopic changes accumulate in its structure. Eventually, a tiny crack appears, most often at a point where stress is concentrated, such as a sharp corner, a hole drilled for a bolt or a scratch left during manufacture. With every further cycle of loading, the crack grows a little longer, while the part continues to perform its function normally. Because the remaining sound metal still carries the load, there may be no visible sign that anything is wrong. Only when the crack has reduced the cross-section so much that the rest of the material can no longer bear the load does the component snap, often suddenly. This hidden progression explains why fatigue has been responsible for many unexpected failures in railway axles, aircraft and bridges. Designers now try to reduce the risk in several ways. They avoid sharp changes in shape, smooth the surfaces of critical parts and estimate how many cycles a component will experience during its working life. In addition, parts that cannot be allowed to fail are inspected at regular intervals with methods, such as ultrasound, that can reveal cracks hidden beneath the surface. The aim is not to prevent every crack from forming, but to find any crack and replace the part long before it becomes dangerous.

It can be inferred from the passage that ----.

Accepted Answer

a part that seems to be working normally may already contain a growing crack

Answer

fatigue is a more serious problem in aircraft than in railway axles or bridges

Answer

cracks that start at a scratch grow more slowly than those that start at a bolt hole

Answer

regular ultrasound inspections can stop fatigue cracks from forming in critical parts

Answer

a part designed to carry a heavy load is unlikely to suffer from fatigue

Question 4

Hydrogen is often described as a promising fuel for a low-carbon future. When it is used in a fuel cell to generate electricity, the only direct by-product is water, and it can be produced without releasing greenhouse gases if the electricity used to split water into hydrogen and oxygen comes from renewable sources. One of the main obstacles to its wider use, however, lies not in producing hydrogen but in storing it. Although a kilogram of hydrogen contains more energy than a kilogram of petrol, hydrogen is the lightest of all elements, and at ordinary temperatures and pressures a given amount of it takes up an enormous volume. To store useful quantities in a vehicle, engineers must therefore compress the gas to very high pressures, which requires thick, strong tanks that add weight and cost. An alternative is to cool hydrogen until it becomes a liquid, but this happens only at around minus 253 degrees Celsius, and cooling it to that temperature consumes a considerable share of the energy that the fuel contains. Even in well-insulated tanks, some of the liquid gradually warms and turns back into gas, which must be released. Hydrogen molecules are also so small that they can slip through materials that hold other gases securely, and in some metals they can cause a loss of strength known as embrittlement. For these reasons, researchers are investigating materials that can absorb hydrogen like a sponge and release it when heated. None of these approaches is yet ideal, and the difficulty of storage helps to explain why hydrogen is still used far more widely in industry than in private cars.

What is the main idea of the passage?

Accepted Answer

Storing hydrogen efficiently remains a major obstacle to its wider use as a fuel.

Answer

Fuel cells produce harmful by-products that limit their use in vehicles.

Answer

Hydrogen cannot be produced without releasing greenhouse gases.

Answer

Hydrogen contains less energy per kilogram than petrol does.

Answer

Liquid hydrogen is the most practical form of the fuel for private cars.

Question 5

Hydrogen is often described as a promising fuel for a low-carbon future. When it is used in a fuel cell to generate electricity, the only direct by-product is water, and it can be produced without releasing greenhouse gases if the electricity used to split water into hydrogen and oxygen comes from renewable sources. One of the main obstacles to its wider use, however, lies not in producing hydrogen but in storing it. Although a kilogram of hydrogen contains more energy than a kilogram of petrol, hydrogen is the lightest of all elements, and at ordinary temperatures and pressures a given amount of it takes up an enormous volume. To store useful quantities in a vehicle, engineers must therefore compress the gas to very high pressures, which requires thick, strong tanks that add weight and cost. An alternative is to cool hydrogen until it becomes a liquid, but this happens only at around minus 253 degrees Celsius, and cooling it to that temperature consumes a considerable share of the energy that the fuel contains. Even in well-insulated tanks, some of the liquid gradually warms and turns back into gas, which must be released. Hydrogen molecules are also so small that they can slip through materials that hold other gases securely, and in some metals they can cause a loss of strength known as embrittlement. For these reasons, researchers are investigating materials that can absorb hydrogen like a sponge and release it when heated. None of these approaches is yet ideal, and the difficulty of storage helps to explain why hydrogen is still used far more widely in industry than in private cars.

According to the passage, hydrogen must be compressed to very high pressures for use in vehicles because ----.

Accepted Answer

a given amount of the gas takes up a very large volume under ordinary conditions

Answer

compression prevents the gas from weakening metals

Answer

compression turns the gas into a liquid at room temperature

Answer

hydrogen contains very little energy per kilogram

Answer

compressed hydrogen can be stored in light, thin tanks

Question 6

Hydrogen is often described as a promising fuel for a low-carbon future. When it is used in a fuel cell to generate electricity, the only direct by-product is water, and it can be produced without releasing greenhouse gases if the electricity used to split water into hydrogen and oxygen comes from renewable sources. One of the main obstacles to its wider use, however, lies not in producing hydrogen but in storing it. Although a kilogram of hydrogen contains more energy than a kilogram of petrol, hydrogen is the lightest of all elements, and at ordinary temperatures and pressures a given amount of it takes up an enormous volume. To store useful quantities in a vehicle, engineers must therefore compress the gas to very high pressures, which requires thick, strong tanks that add weight and cost. An alternative is to cool hydrogen until it becomes a liquid, but this happens only at around minus 253 degrees Celsius, and cooling it to that temperature consumes a considerable share of the energy that the fuel contains. Even in well-insulated tanks, some of the liquid gradually warms and turns back into gas, which must be released. Hydrogen molecules are also so small that they can slip through materials that hold other gases securely, and in some metals they can cause a loss of strength known as embrittlement. For these reasons, researchers are investigating materials that can absorb hydrogen like a sponge and release it when heated. None of these approaches is yet ideal, and the difficulty of storage helps to explain why hydrogen is still used far more widely in industry than in private cars.

It can be inferred from the passage that liquid hydrogen ----.

Accepted Answer

cannot be kept in a tank indefinitely without some of it being lost

Answer

can be produced without using any energy for cooling

Answer

is produced mainly from petrol in industrial plants

Answer

is easier to store than compressed hydrogen because it needs no insulation

Answer

has become the standard fuel for private cars because of its high energy content

Question 7

Hydrogen is often described as a promising fuel for a low-carbon future. When it is used in a fuel cell to generate electricity, the only direct by-product is water, and it can be produced without releasing greenhouse gases if the electricity used to split water into hydrogen and oxygen comes from renewable sources. One of the main obstacles to its wider use, however, lies not in producing hydrogen but in storing it. Although a kilogram of hydrogen contains more energy than a kilogram of petrol, hydrogen is the lightest of all elements, and at ordinary temperatures and pressures a given amount of it takes up an enormous volume. To store useful quantities in a vehicle, engineers must therefore compress the gas to very high pressures, which requires thick, strong tanks that add weight and cost. An alternative is to cool hydrogen until it becomes a liquid, but this happens only at around minus 253 degrees Celsius, and cooling it to that temperature consumes a considerable share of the energy that the fuel contains. Even in well-insulated tanks, some of the liquid gradually warms and turns back into gas, which must be released. Hydrogen molecules are also so small that they can slip through materials that hold other gases securely, and in some metals they can cause a loss of strength known as embrittlement. For these reasons, researchers are investigating materials that can absorb hydrogen like a sponge and release it when heated. None of these approaches is yet ideal, and the difficulty of storage helps to explain why hydrogen is still used far more widely in industry than in private cars.

The word 'considerable' in the passage is closest in meaning to ----.

Accepted Answer

significant

Answer

predictable

Answer

constant

Answer

negligible

Answer

temporary

Question 8

Climate scientists agree that reducing atmospheric carbon dioxide is of great importance for future generations, since rising temperatures at a global level threaten both physical ecosystems and human health. Effective strategies must include not only renewable energy but also carbon capture technologies, which extract carbon dioxide from industrial emissions before it can spread into the atmosphere. NASA satellite observations help researchers study atmospheric carbon dioxide and its sources and sinks. In the middle of this transition, however, a missing piece remains: affordable storage solutions for captured carbon. The passage uses an analogy: burying drugs underground without checking their long-term chemical stability. This comparison highlights why the safety and durability of storage must be assessed carefully. Each proposed storage method requires careful assessment before large-scale deployment. Without addressing this gap, ambitious emission targets may remain theoretical rather than practical, leaving the case for carbon capture incomplete despite its promising potential.

What is the main idea of the passage?

Accepted Answer

Reducing carbon requires both technology and unresolved storage solutions

Answer

NASA satellites are the only reliable tool for tracking emissions

Answer

Carbon capture technology is fully developed and ready for global use

Answer

Physical ecosystems are no longer affected by rising temperatures

Answer

Renewable energy has replaced the need for carbon capture entirely

Question 9

Climate scientists agree that reducing atmospheric carbon dioxide is of great importance for future generations, since rising temperatures at a global level threaten both physical ecosystems and human health. Effective strategies must include not only renewable energy but also carbon capture technologies, which extract carbon dioxide from industrial emissions before it can spread into the atmosphere. NASA satellite observations help researchers study atmospheric carbon dioxide and its sources and sinks. In the middle of this transition, however, a missing piece remains: affordable storage solutions for captured carbon. The passage uses an analogy: burying drugs underground without checking their long-term chemical stability. This comparison highlights why the safety and durability of storage must be assessed carefully. Each proposed storage method requires careful assessment before large-scale deployment. Without addressing this gap, ambitious emission targets may remain theoretical rather than practical, leaving the case for carbon capture incomplete despite its promising potential.

According to the passage, what is described as a 'missing piece'?

Accepted Answer

Affordable and stable carbon storage methods

Answer

Global temperature monitoring systems

Answer

Renewable energy infrastructure

Answer

Satellite technology for measuring emissions

Answer

Government policies on emissions reduction

Question 10

Climate scientists agree that reducing atmospheric carbon dioxide is of great importance for future generations, since rising temperatures at a global level threaten both physical ecosystems and human health. Effective strategies must include not only renewable energy but also carbon capture technologies, which extract carbon dioxide from industrial emissions before it can spread into the atmosphere. NASA satellite observations help researchers study atmospheric carbon dioxide and its sources and sinks. In the middle of this transition, however, a missing piece remains: affordable storage solutions for captured carbon. The passage uses an analogy: burying drugs underground without checking their long-term chemical stability. This comparison highlights why the safety and durability of storage must be assessed carefully. Each proposed storage method requires careful assessment before large-scale deployment. Without addressing this gap, ambitious emission targets may remain theoretical rather than practical, leaving the case for carbon capture incomplete despite its promising potential.

What can be inferred about the comparison to 'drugs buried underground'?

Accepted Answer

The comparison emphasizes the need to assess long-term storage risks

Answer

Carbon storage is scientifically proven to be completely safe

Answer

Researchers fully support underground storage without hesitation

Answer

Drugs and carbon dioxide have identical chemical properties

Answer

This comparison proves storage technology is obsolete

Question 11

Climate scientists agree that reducing atmospheric carbon dioxide is of great importance for future generations, since rising temperatures at a global level threaten both physical ecosystems and human health. Effective strategies must include not only renewable energy but also carbon capture technologies, which extract carbon dioxide from industrial emissions before it can spread into the atmosphere. NASA satellite observations help researchers study atmospheric carbon dioxide and its sources and sinks. In the middle of this transition, however, a missing piece remains: affordable storage solutions for captured carbon. The passage uses an analogy: burying drugs underground without checking their long-term chemical stability. This comparison highlights why the safety and durability of storage must be assessed carefully. Each proposed storage method requires careful assessment before large-scale deployment. Without addressing this gap, ambitious emission targets may remain theoretical rather than practical, leaving the case for carbon capture incomplete despite its promising potential.

What does the word 'effective' most likely mean in this context?

Accepted Answer

Producing the desired results successfully

Answer

Expensive and complicated

Answer

Related only to satellite monitoring

Answer

Temporary and unreliable

Answer

Focused solely on renewable energy

Question 12

Many of the world's largest caves have been carved out of limestone, a rock composed mainly of calcium carbonate. What makes limestone unusual is that it dissolves fairly easily in slightly acidic water, so caves in this rock are formed mainly by chemical reactions rather than by physical forces such as flowing water or grinding ice. The process begins when rainwater absorbs carbon dioxide from the air and, more importantly, from the soil, where decaying plant matter releases large amounts of the gas. The result is a weak acid that seeps downward through cracks in the rock. As it moves, the acid reacts with the calcium carbonate and carries it away in solution, gradually widening the cracks into channels and, over hundreds of thousands of years, into passages large enough for people to walk through. Landscapes shaped in this way, known as karst, often have few streams on the surface, because rainwater disappears quickly into the ground. Instead, they are marked by sinkholes, underground rivers and springs where the water eventually returns to the surface. The same chemistry that creates caves can also decorate them. When water rich in dissolved calcium carbonate drips from a cave ceiling, it releases some of its carbon dioxide into the cave air. This causes a small amount of the mineral to come out of solution and form a thin deposit. Drop by drop, these deposits build up into the icicle-like formations that hang from the ceiling and the stalagmites that rise from the floor. Because karst regions allow water to travel quickly underground with little natural filtering, pollution released at the surface can reach springs and wells far more easily than in other types of terrain.

The passage mainly discusses ----.

Accepted Answer

the chemical processes by which limestone is dissolved to form caves and related features of the landscape

Answer

the role of flowing water and ice in shaping most types of rock

Answer

the ways in which karst regions can be protected from pollution

Answer

the dangers that underground rivers pose to people exploring caves

Answer

the reasons why limestone is the most common rock on Earth

Question 13

Many of the world's largest caves have been carved out of limestone, a rock composed mainly of calcium carbonate. What makes limestone unusual is that it dissolves fairly easily in slightly acidic water, so caves in this rock are formed mainly by chemical reactions rather than by physical forces such as flowing water or grinding ice. The process begins when rainwater absorbs carbon dioxide from the air and, more importantly, from the soil, where decaying plant matter releases large amounts of the gas. The result is a weak acid that seeps downward through cracks in the rock. As it moves, the acid reacts with the calcium carbonate and carries it away in solution, gradually widening the cracks into channels and, over hundreds of thousands of years, into passages large enough for people to walk through. Landscapes shaped in this way, known as karst, often have few streams on the surface, because rainwater disappears quickly into the ground. Instead, they are marked by sinkholes, underground rivers and springs where the water eventually returns to the surface. The same chemistry that creates caves can also decorate them. When water rich in dissolved calcium carbonate drips from a cave ceiling, it releases some of its carbon dioxide into the cave air. This causes a small amount of the mineral to come out of solution and form a thin deposit. Drop by drop, these deposits build up into the icicle-like formations that hang from the ceiling and the stalagmites that rise from the floor. Because karst regions allow water to travel quickly underground with little natural filtering, pollution released at the surface can reach springs and wells far more easily than in other types of terrain.

According to the passage, the soil contributes to the formation of limestone caves by ----.

Accepted Answer

supplying much of the carbon dioxide that turns rainwater into a weak acid

Answer

absorbing rainwater and preventing it from seeping into the rock

Answer

releasing the calcium carbonate that is later deposited on cave ceilings

Answer

filling the cracks in the rock so that water cannot pass through

Answer

filtering pollution out of the water before it reaches underground rivers

Question 14

Many of the world's largest caves have been carved out of limestone, a rock composed mainly of calcium carbonate. What makes limestone unusual is that it dissolves fairly easily in slightly acidic water, so caves in this rock are formed mainly by chemical reactions rather than by physical forces such as flowing water or grinding ice. The process begins when rainwater absorbs carbon dioxide from the air and, more importantly, from the soil, where decaying plant matter releases large amounts of the gas. The result is a weak acid that seeps downward through cracks in the rock. As it moves, the acid reacts with the calcium carbonate and carries it away in solution, gradually widening the cracks into channels and, over hundreds of thousands of years, into passages large enough for people to walk through. Landscapes shaped in this way, known as karst, often have few streams on the surface, because rainwater disappears quickly into the ground. Instead, they are marked by sinkholes, underground rivers and springs where the water eventually returns to the surface. The same chemistry that creates caves can also decorate them. When water rich in dissolved calcium carbonate drips from a cave ceiling, it releases some of its carbon dioxide into the cave air. This causes a small amount of the mineral to come out of solution and form a thin deposit. Drop by drop, these deposits build up into the icicle-like formations that hang from the ceiling and the stalagmites that rise from the floor. Because karst regions allow water to travel quickly underground with little natural filtering, pollution released at the surface can reach springs and wells far more easily than in other types of terrain.

It can be inferred from the passage that ----.

Accepted Answer

a spring in a karst region may be polluted by waste released some distance away

Answer

karst regions are usually crossed by a dense network of surface streams

Answer

cave formations grow when dripping water absorbs carbon dioxide from the cave air

Answer

caves in limestone are shaped mainly by grinding ice rather than by chemical reactions

Answer

limestone passages large enough to walk through can form within a few decades

Question 15

Many of the world's largest caves have been carved out of limestone, a rock composed mainly of calcium carbonate. What makes limestone unusual is that it dissolves fairly easily in slightly acidic water, so caves in this rock are formed mainly by chemical reactions rather than by physical forces such as flowing water or grinding ice. The process begins when rainwater absorbs carbon dioxide from the air and, more importantly, from the soil, where decaying plant matter releases large amounts of the gas. The result is a weak acid that seeps downward through cracks in the rock. As it moves, the acid reacts with the calcium carbonate and carries it away in solution, gradually widening the cracks into channels and, over hundreds of thousands of years, into passages large enough for people to walk through. Landscapes shaped in this way, known as karst, often have few streams on the surface, because rainwater disappears quickly into the ground. Instead, they are marked by sinkholes, underground rivers and springs where the water eventually returns to the surface. The same chemistry that creates caves can also decorate them. When water rich in dissolved calcium carbonate drips from a cave ceiling, it releases some of its carbon dioxide into the cave air. This causes a small amount of the mineral to come out of solution and form a thin deposit. Drop by drop, these deposits build up into the icicle-like formations that hang from the ceiling and the stalagmites that rise from the floor. Because karst regions allow water to travel quickly underground with little natural filtering, pollution released at the surface can reach springs and wells far more easily than in other types of terrain.

The word 'it' in the sentence beginning 'When water rich in dissolved calcium carbonate' refers to ----.

Accepted Answer

water

Answer

the cave air

Answer

the cave ceiling

Answer

carbon dioxide

Answer

calcium carbonate

Question 16

One of the most difficult problems in astronomy is measuring how far away objects in space are. A star that appears faint may be a dim star that is relatively close or a very bright star that is extremely distant, and a telescope cannot tell these possibilities apart simply by looking. To solve this problem, astronomers need what they call standard candles: objects whose true brightness is known, so that their distance can be calculated from how bright they appear. Some of the most useful standard candles are stars known as Cepheid variables. These stars expand and contract regularly, and as they do so, their brightness rises and falls in a steady rhythm that may last from about a day to several months. Early in the twentieth century, astronomers discovered that the length of this cycle is closely linked to a Cepheid's true brightness: the more luminous the star, the more slowly it pulsates. This relationship made it possible to determine a Cepheid's actual brightness just by timing its pulses. By comparing that value with the star's apparent brightness, astronomers could work out its distance. Cepheids later allowed them to show that some faint patches of light in the sky were not clouds within our own galaxy but entire separate galaxies lying far beyond it. The method has limits, however. Dust between the star and the observer dims its light and can make it seem farther away than it really is, so measurements must be corrected carefully. In addition, even the brightest Cepheids become too faint to observe in the most distant galaxies, where other standard candles must be used.

The primary purpose of the passage is to ----.

Accepted Answer

explain how a type of pulsating star helps astronomers measure distances in space

Answer

show why dust makes the distances of Cepheids impossible to measure accurately

Answer

describe the physical processes that cause Cepheid stars to expand and contract

Answer

compare the accuracy of Cepheids with that of other kinds of standard candles

Answer

explain why the faintest stars in the night sky are usually the most distant

Question 17

One of the most difficult problems in astronomy is measuring how far away objects in space are. A star that appears faint may be a dim star that is relatively close or a very bright star that is extremely distant, and a telescope cannot tell these possibilities apart simply by looking. To solve this problem, astronomers need what they call standard candles: objects whose true brightness is known, so that their distance can be calculated from how bright they appear. Some of the most useful standard candles are stars known as Cepheid variables. These stars expand and contract regularly, and as they do so, their brightness rises and falls in a steady rhythm that may last from about a day to several months. Early in the twentieth century, astronomers discovered that the length of this cycle is closely linked to a Cepheid's true brightness: the more luminous the star, the more slowly it pulsates. This relationship made it possible to determine a Cepheid's actual brightness just by timing its pulses. By comparing that value with the star's apparent brightness, astronomers could work out its distance. Cepheids later allowed them to show that some faint patches of light in the sky were not clouds within our own galaxy but entire separate galaxies lying far beyond it. The method has limits, however. Dust between the star and the observer dims its light and can make it seem farther away than it really is, so measurements must be corrected carefully. In addition, even the brightest Cepheids become too faint to observe in the most distant galaxies, where other standard candles must be used.

According to the passage, astronomers can determine the true brightness of a Cepheid by ----.

Accepted Answer

timing the length of its cycle of brightening and dimming

Answer

measuring the amount of dust between the star and the observer

Answer

comparing it with nearby stars whose distances are already known

Answer

observing the galaxy in which the star is located

Answer

measuring how bright the star appears in the night sky

Question 18

One of the most difficult problems in astronomy is measuring how far away objects in space are. A star that appears faint may be a dim star that is relatively close or a very bright star that is extremely distant, and a telescope cannot tell these possibilities apart simply by looking. To solve this problem, astronomers need what they call standard candles: objects whose true brightness is known, so that their distance can be calculated from how bright they appear. Some of the most useful standard candles are stars known as Cepheid variables. These stars expand and contract regularly, and as they do so, their brightness rises and falls in a steady rhythm that may last from about a day to several months. Early in the twentieth century, astronomers discovered that the length of this cycle is closely linked to a Cepheid's true brightness: the more luminous the star, the more slowly it pulsates. This relationship made it possible to determine a Cepheid's actual brightness just by timing its pulses. By comparing that value with the star's apparent brightness, astronomers could work out its distance. Cepheids later allowed them to show that some faint patches of light in the sky were not clouds within our own galaxy but entire separate galaxies lying far beyond it. The method has limits, however. Dust between the star and the observer dims its light and can make it seem farther away than it really is, so measurements must be corrected carefully. In addition, even the brightest Cepheids become too faint to observe in the most distant galaxies, where other standard candles must be used.

It can be inferred from the passage that ----.

Accepted Answer

uncorrected dust would lead astronomers to overestimate a Cepheid's distance

Answer

Cepheids that pulsate quickly are more luminous than those that pulsate slowly

Answer

Cepheid variables are the only standard candles that astronomers use

Answer

all the faint patches of light in the sky turned out to be separate galaxies

Answer

Cepheids can be observed even in the most distant galaxies

Question 19

Radio telescopes detect the faint radio waves given off by distant objects such as galaxies, clouds of gas and the remains of exploded stars. Because radio waves are far longer than the waves of visible light, a radio telescope must be enormous to produce sharp images: the amount of detail an instrument can capture depends on the size of its collecting surface compared with the wavelength it observes. A single dish large enough to match the sharpness of an ordinary optical telescope could never be built, since the structure would collapse under its own weight long before it reached the required size. Astronomers overcome this limitation with a technique known as interferometry. Instead of relying on one giant dish, they link several smaller antennas spread across a wide area and record the signals arriving at each of them. Since a radio wave from a distant source reaches each antenna at a slightly different moment, these tiny delays can be measured and used by computers to reconstruct an image. In effect, the network behaves like a single telescope whose diameter equals the greatest distance between its antennas. The farther apart the antennas are placed, the finer the details that can be resolved. This principle has allowed astronomers to combine observatories on different continents and to produce images of the region immediately surrounding a black hole. The technique, however, makes heavy demands of its own. Each antenna must record the precise time at which signals arrive, which requires extremely accurate atomic clocks, and the enormous quantities of data must often be transported on physical storage devices because they are too large to send over ordinary networks.

What is the passage mainly about?

Accepted Answer

How linking separate antennas allows astronomers to overcome the size limits of single radio telescopes

Answer

How astronomers transport data between observatories on different continents

Answer

Why optical telescopes produce sharper images than any radio instrument can

Answer

How atomic clocks have changed the way astronomers measure distances in space

Answer

Why radio waves are more useful than visible light for studying black holes

Question 20

Radio telescopes detect the faint radio waves given off by distant objects such as galaxies, clouds of gas and the remains of exploded stars. Because radio waves are far longer than the waves of visible light, a radio telescope must be enormous to produce sharp images: the amount of detail an instrument can capture depends on the size of its collecting surface compared with the wavelength it observes. A single dish large enough to match the sharpness of an ordinary optical telescope could never be built, since the structure would collapse under its own weight long before it reached the required size. Astronomers overcome this limitation with a technique known as interferometry. Instead of relying on one giant dish, they link several smaller antennas spread across a wide area and record the signals arriving at each of them. Since a radio wave from a distant source reaches each antenna at a slightly different moment, these tiny delays can be measured and used by computers to reconstruct an image. In effect, the network behaves like a single telescope whose diameter equals the greatest distance between its antennas. The farther apart the antennas are placed, the finer the details that can be resolved. This principle has allowed astronomers to combine observatories on different continents and to produce images of the region immediately surrounding a black hole. The technique, however, makes heavy demands of its own. Each antenna must record the precise time at which signals arrive, which requires extremely accurate atomic clocks, and the enormous quantities of data must often be transported on physical storage devices because they are too large to send over ordinary networks.

According to the passage, a single radio dish as sharp as an ordinary optical telescope cannot be built because ----.

Accepted Answer

such a structure would collapse under its own weight before reaching the necessary size

Answer

a single dish could not record the arrival time of signals precisely enough

Answer

the data produced by such a dish would be too large to transport

Answer

radio waves are much shorter than the waves of visible light

Answer

radio waves are too weak to be collected by one dish, however large it is

Question 21

Radio telescopes detect the faint radio waves given off by distant objects such as galaxies, clouds of gas and the remains of exploded stars. Because radio waves are far longer than the waves of visible light, a radio telescope must be enormous to produce sharp images: the amount of detail an instrument can capture depends on the size of its collecting surface compared with the wavelength it observes. A single dish large enough to match the sharpness of an ordinary optical telescope could never be built, since the structure would collapse under its own weight long before it reached the required size. Astronomers overcome this limitation with a technique known as interferometry. Instead of relying on one giant dish, they link several smaller antennas spread across a wide area and record the signals arriving at each of them. Since a radio wave from a distant source reaches each antenna at a slightly different moment, these tiny delays can be measured and used by computers to reconstruct an image. In effect, the network behaves like a single telescope whose diameter equals the greatest distance between its antennas. The farther apart the antennas are placed, the finer the details that can be resolved. This principle has allowed astronomers to combine observatories on different continents and to produce images of the region immediately surrounding a black hole. The technique, however, makes heavy demands of its own. Each antenna must record the precise time at which signals arrive, which requires extremely accurate atomic clocks, and the enormous quantities of data must often be transported on physical storage devices because they are too large to send over ordinary networks.

It can be inferred from the passage that ----.

Accepted Answer

an array whose antennas are only a short distance apart captures less detail than one whose antennas are widely separated

Answer

interferometry works only when all the antennas are located on the same continent

Answer

without atomic clocks, radio telescopes could not detect radio waves at all

Answer

images of the region around a black hole can be produced with a single optical telescope

Answer

the sharpness of an image depends mainly on the number of antennas rather than on the distance between them

Question 22

Radio telescopes detect the faint radio waves given off by distant objects such as galaxies, clouds of gas and the remains of exploded stars. Because radio waves are far longer than the waves of visible light, a radio telescope must be enormous to produce sharp images: the amount of detail an instrument can capture depends on the size of its collecting surface compared with the wavelength it observes. A single dish large enough to match the sharpness of an ordinary optical telescope could never be built, since the structure would collapse under its own weight long before it reached the required size. Astronomers overcome this limitation with a technique known as interferometry. Instead of relying on one giant dish, they link several smaller antennas spread across a wide area and record the signals arriving at each of them. Since a radio wave from a distant source reaches each antenna at a slightly different moment, these tiny delays can be measured and used by computers to reconstruct an image. In effect, the network behaves like a single telescope whose diameter equals the greatest distance between its antennas. The farther apart the antennas are placed, the finer the details that can be resolved. This principle has allowed astronomers to combine observatories on different continents and to produce images of the region immediately surrounding a black hole. The technique, however, makes heavy demands of its own. Each antenna must record the precise time at which signals arrive, which requires extremely accurate atomic clocks, and the enormous quantities of data must often be transported on physical storage devices because they are too large to send over ordinary networks.

The word 'they' in the last sentence of the passage refers to ----.

Accepted Answer

the enormous quantities of data

Answer

atomic clocks

Answer

ordinary networks

Answer

the antennas

Answer

physical storage devices

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