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# CAT 2021 Reading Comprehension Solution 10

[PASSAGE]

Direction for Reading Comprehension: The passages given here are followed by some questions that have four answer choices; read the passage carefully and pick the option whose answer best aligns with the passage.

Keeping time accurately comes with a price. The maximum accuracy of a clock is directly related to how much disorder, or entropy, it creates every time it ticks. Natalia Ares at the University of Oxford and her colleagues made this discovery using a tiny clock with an accuracy that can be controlled. The clock consists of a 50-nanometre-thick membrane of silicon nitride, vibrated by an electric current. Each time the membrane moved up and down once and then returned to its original position, the researchers counted a tick, and the regularity of the spacing between the ticks represented the accuracy of the clock. The researchers found that as they increased the clock's accuracy, the heat produced in the system grew, increasing the entropy of its surroundings by jostling nearby particles . . . "If a clock is more accurate, you are paying for it somehow," says Ares. In this case, you pay for it by pouring more ordered energy into the clock, which is then converted into entropy. "By measuring time, we are increasing the entropy of the universe," says Ares. The more entropy there is in the universe, the closer it may be to its eventual demise. "Maybe we should stop measuring time," says Ares. The scale of the additional entropy is so small, though, that there is no need to worry about its effects, she says.

The increase in entropy in timekeeping may be related to the "arrow of time", says Marcus Huber at the Austrian Academy of Sciences in Vienna, who was part of the research team. It has been suggested that the reason that time only flows forward, not in reverse, is that the total amount of entropy in the universe is constantly increasing, creating disorder that cannot be put in order again.

The relationship that the researchers found is a limit on the accuracy of a clock, so it doesn't mean that a clock that creates the most possible entropy would be maximally accurate - hence a large, inefficient grandfather clock isn't more precise than an atomic clock. "It's a bit like fuel use in a car. Just because I'm using more fuel doesn't mean that I'm going faster or further," says Huber.

When the researchers compared their results with theoretical models developed for clocks that rely on quantum effects, they were surprised to find that the relationship between accuracy and entropy seemed to be the same for both. . . . We can't be sure yet that these results are actually universal, though, because there are many types of clocks for which the relationship between accuracy and entropy haven't been tested. "It's still unclear how this principle plays out in real devices such as atomic clocks, which push the ultimate quantum limits of accuracy," says Mark Mitchison at Trinity College Dublin in Ireland. Understanding this relationship could be helpful for designing clocks in the future, particularly those used in quantum computers and other devices where both accuracy and temperature are crucial, says Ares. This finding could also help us understand more generally how the quantum world and the classical world are similar and different in terms of thermodynamics and the passage of time.

Question: 1

Which one of the following sets of words and phrases serves best as keywords of the passage?

1. Electric current; Heat; Quantum effects.

2. Silicon Nitride; Energy; Grandfather Clock.

3. Measuring Time; Accuracy; Entropy.

4. Membrane; Arrow of time; Entropy.

Option: 3
Solution:

This is a very simple question. We have to pick the option that has the keywords. Measuring time is the first keyword that we can derive from the first paragraph. The second half of the passage discusses entropy. Thus option 3 is the best answer.

Question: 2

The author makes all of the following arguments in the passage, EXCEPT that:

1. The relationship between accuracy and entropy may not apply to all clocks.

2. Researchers found that the heat produced in a system is the price paid for increased accuracy of measurement.

3. There is no difference in accuracy between an inefficient grandfather clock and an atomic clock.

4. In designing clocks for quantum computers, both precision and heat have to be taken into account.

Option: 2
Solution:

This question has been challenged by our team and also by many students, including IMS. This question is contentious.

Question: 3

None of the following statements can be inferred from the passage EXCEPT that:

1. the arrow of time has not yet been tested for atomic clocks.

2. quantum computers are likely to produce more heat and, hence, more entropy, because of the emphasis on their clocks' accuracy.

3. grandfather clocks are likely to produce less heat and, hence, less entropy, because they are not as accurate.

4. a clock with a 50-nanometre-thick membrane of silicon nitride has been made to vibrate, producing electric currents.

Option: 2
Solution:

This is a moderate difficulty question. We have to pick the choice that cannot be inferred. Two options can be checked by understanding the idea of "arrow of time", which according to the passage, means time always moves forward because of increasing entropy in the universe... But the idea of entropy vs accuracy has not yet been understood as to how it plays out for atomic clocks, suggesting that arrow of time must have been tested on atomic clocks. That's why you don't understand how arrow of time plays out in atomic clocks. Thus 1 cannot be inferred, as the opposite of 1 is true. 3 cannot be inferred because the passage talks opposite of this. 4 cannot be inferred because it fed with electric currents, not producing electric currents. Thus 1, 3 and 4 cannot be inferred. 2 can be inferred from last paragraph.

Question: 4

"It's a bit like fuel use in a car. Just because I'm using more fuel doesn't mean that I'm going faster or further . . ." What is the purpose of this example?

1. If you go faster in a car, you will tend to consume more fuel, but the converse is not necessarily true. In the same way, increased entropy does not necessarily mean greater accuracy of a clock.

2. The further you go in a car, the more fuel you use. In the same way, the faster you go in a car, the less time you use.

3. If you measure the speed of a car with a grandfather clock, the result will be different than if you measured it with an atomic clock.

4. The further and faster you go in a car, the greater the amount of fuel you will use, the greater the amount of heat produced and, hence, the greater the entropy.

Option: 1
Solution:

This is an easy question; you just have to focus on the paragraph where this sentence has come. Option 1 accurately captures this. Entropy and fuel are analogous, higher entropy doesn't always mean higher accuracy, just as higher fuel consumption in a car doesn't mean greater speed.

### CAT 2021 RC passage with solution

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