GRE Test explanations for Reading comprehension

Directions: Each passage in this group is followed by questions based on its content. After reading a passage, choose the best answer for each question. Answer all questions following a passage on the basis of what is stated or implied in that passage.

It has been known for many decades that the appearance of sunspots is roughly periodic, with an average cycle of eleven years. Moreover, the incidence of solar flares and the flux of solar cosmic rays, ultraviolet radiation, and x-radiation all vary directly with the sunspot cycle. But after more than a century of investigation, the relation of these and other phenomena, known collectively as the solar-activity cycle, to terrestrial weather and climate remains unclear. For example, the sunspot cycle and the allied magnetic-polarity cycle have been stable as rainfall, temperature, and winds. Invariably, however, the relation is weak, and usually of dubious statistical significance.

Information about the effects of solar variability over longer terms has also been sought. The absence of recorded sunspot activity in the notes kept by European observers in the late seventeenth and early eighteenth centuries has led some scholars to postulate a brief cessation of sunspot activity at that time (a period called the Maunder minimum). The Maunder minimum has been linked to a span of unusual cold in Europe extending from the sixteenth to the early nineteenth centuries. The reality of the Maunder minimum has yet to be established, however, especially since the records that Chinese naked eye observers of solar activity made at that time appear to contradict it. Scientists have also sought evidence of long-term solar periodicities by examining indirect climatological data, such as fossil records of the thickness of ancient tree rings. These studies, however, failed to link unequivocally terrestrial climate and the solar-activity cycle, or even to confirm the cycle's past existence.

If consistent and reliable geological or archaeological evidence tracing the solar-activity cycle in the distant past could be found, it might also resolve an important issue in solar physics: how to model solar activity. Currently, there are two models of solar activity. The first supposes that the Sun's internal motions (caused by rotation and convection) interact with its large-scale magnetic field to produce a dynamo, a device in which mechanical energy is converted into the energy of a magnetic field. In short, the Sun's large-scale magnetic field is taken to be self-sustaining, so that the solar-activity cycle it drives would be maintained with little overall change for perhaps billions of years. The alternative explanation supposes that the Sun's large-scale magnetic field is a remnant of the field the Sun acquired when it formed, and is not sustained against decay. In this model, the solar mechanism dependent on the Sun's magnetic field runs down more quickly. Thus, the characteristics of the solar-activity cycle could be expected to change over a long period of time. Modern solar observations span too short a time to reveal whether present cyclical solar activity is a long-lived feature of the Sun, or merely a transient phenomenon.

The author focuses primarily on

(A) Presenting two competing scientific theories concerning solar activity and evaluating geological evidence often cited to support them.

(B) Giving a brief overview of some recent scientific developments in solar physics and assessing their impact on future climatological research.

(C) Discussing the difficulties involved in linking terrestrial phenomena with solar activity and indicating how resolving that issue could have an impact on our understanding of solar physics.

(D) Pointing out the futility of a certain line of scientific inquiry into the terrestrial effects of solar activity and recommending its abandonment in favor of purely physics-oriented research.

(E) Outlining the specific reasons why a problem in solar physics has not yet been solved and faulting the overly theoretical approach of modern physicists.

Explanation:

The question is a primary purpose or main idea question. The general outline of the main idea of a passage can usually be discerned by reading the initial parts of the paragraph and the concluding part of the passage.

(A) These are no two competing scientific theories concerning solar activity in the passage. The two models of solar activity mentioned in the third passage cannot be mistaken to be two theories concerning solar spot activity and its correlation with phenomena and earth. No geological evidence is cited in support of the two models. Rather author wishes that geological evidence tracing the solar activity cycle, (not the models of solar activity) would be found.

(B) There are no new or recent developments in solar physics mentioned in neither the passage nor a brief overview given of these given. Therefore the question of assessing their impact on future climatological research does not arise.

(C) The first two paragraphs discuss the difficulty faced in correlating the solar cycle activity and terrestrial phenomena. The third paragraph indicates how specifically ascertaining the solar activity cycle would solve an important problem in solar physics that of how to model solar activity.

(D) The first two paragraphs do make clear that there is indeed little correlation between observed solar activity and terrestrial phenomena. Nowhere does the author say that this line of enquiry that tries to understand the terrestrial effect of solar activity is futile or useless. The author also does not suggest abandoning this line of enquiry in favor of purely physics oriented research. He merely mentions that a problem in solar physics could be solved if definite pattern of solar activity were to be found.

(E) This choice speaks only about why a problem mentioned in the third paragraph in solar physics has not been solved yet; the problem of modeling solar activity. This is because, there is no consistent and reliable geological or archaeological evidence tracing the solar activity cycle.

The correct answer is option C.

Percent correctly answered: 63.

Which of the following statements about the two models of solar activity, as they are described in lines 37-55, is accurate?

(A) In both models cyclical solar activity is regarded as a long-lived feature of the Sun, persisting with little change over billions of years.

(B) In both models the solar-activity cycle is hypothesized as being dependent on the large-scale solar magnetic field.

(C) In one model the Sun's magnetic field is thought to play a role in causing solar activity, whereas in the other model it is not.

(D) In one model solar activity is presumed to be unrelated to terrestrial phenomena, whereas in the other model solar activity is though to have observable effects on the Earth.

(E) In one model cycles of solar activity with periodicities longer than a few decades are considered to be impossible, whereas in the other model such cycles are predicted.

Explanation:

This is a direct question.

(A) While it is true to say that in both model solar activity is a long lived feature of the Sun, it is incorrect to say that in both models solar activity persisted with little as no change over billions of years. This is time for the first model only. Ina the alternative model, the author states that the characteristics of the solar activity cycle could be expected to change over a long period of time.

(B) In the first model the solar-activity cycle is generated when the sun's internal motion interact with the sun's large-scale magnetic field. This produces a dynamo, a device in which mechanical energy is converted into the energy of a magnetic field. The passage states that, solar activity depends on the magnetic field. The second model is thought to have originated when the sun formed. In this model also solar activity is dependent sun's magnetic field.

(C) In both models it is the sun's magnetic field plays the causative sole in solar activity. The differences between the two models concern the origins of the sun's magnetic field which drives the solar activity cycle.

(D) The passage states that, the model of solar activity could be constructed if reliable and consistent geological as archaeological evidence trains the solar activity cycle of the distant past is found. This fact applies to both the models. Finding terrestrial evidence would solve the problem of how to model the solar activity. There are two models of solar activity, and there might have been any number of them. All of these models would be dependent for verification on the terrestrial evidence.

(E) The passage no where says that in none model of solar activity long time periods between solar activity cycles are considered impossible, and in the other that such long time period longer than a few decades in fact will occur. The current solar activity period is stated to be eleven years. Whether this cyclical period is long lived or temporary feature of solar activity is uncertain.

The correct answer is option B.

Percent correctly answered: 63.

According to the passage, late seventeenth-and early eighteenth-century Chinese records are important for which of the following reasons?
(A) They suggest that the data on which the Maunder minimum was predicated were incorrect.
(B) They suggest that the Maunder minimum cannot be related to climate.
(C) They suggest that the Maunder minimum might be valid only for Europe.
(D) They establish the existence of a span of unusually cold weather worldwide at the time of the Maunder minimum.
(E) They establish that solar activity at the time of the Maunder minimum did not significantly vary from its present pattern.

Explanation:

This is a direct question about the Chinese records of observations of solar activity.

(A) Some scholars theorized that since there were no records of sun spot activity by European observers of the phenomenon, there was a temporary break or inactivity of sun spot activity, which was called the Maunder minimum. The Chinese recorded solar activity during the time of the Maunder minimum, which contradicted the theory that data or the back of it on which scholars postulated the Maunder minimum were incorrect. Therefore the Chinese records are important.

(B) Climatologically data which the scientists examined and the Chinese records of the late seventeenth and early eighteenth century are unrelated.

(C) It is incorrect to state that since the Chinese observed sunspot activity, that this solar activity is not valid for Europe. To state that the cessation of solar activity called the Maunder minimum is applicable only to Europe is absord. Sun spot activity takes place in the Sun irrespective of what geographical regions exist on the earth.

(D) The Chinese naked eye observations of sunspot activity in fact contradict the theory of the Maunder minimum, which states that there was a cessation of sunspot activity for some time. The Maunder minimum correlated with a span of unusually cold weather in Europe. Since the Chinese records contradict the maunder minimum there is no question of establishing what was thought to be the effect of the Maunder minimum locally in Europe, much less worldwide.

(E) The Chinese records do not indicate the time period of the sun spot cycle. Therefore it cannot be concluded that the solar activity at the time of the Maunder minimum did not differ significantly from the present pattern of an eleven-year cycle.

The correct answer is option A.

Percent correctly answered: 64.

It can be inferred from the passage that the argument in favor of the model described in lines 37-45 would be strengthened if which of the following were found to be true?
(A) Episodes of intense volcanic eruptions in the distant past occurred in cycles having very long periodicities.
(B) At the present time the global level of thunderstorm activity increases and decreases in cycles with periodicities of approximately 11 years.
(C) In the distant past cyclical climatic changes had periodicities of longer than 200 years.
(D) In the last century the length of the sunspot cycle has been known to vary by as much as 2 years from its average periodicity of 11 years.
(E) Hundreds of millions of years ago, solar-activity cycles displayed the same periodicities as do present-day solar-activity cycles.

Explanation:

The argument mentioned in the specific lines is that of a self-sustaining magnetic field of the sun, virtually undisturbed over billions of years.

(A) To state that when the time span between solar cycles was long intense volcanic activity was evident during solar activity does not in any way prone that solar cycle activity has remained unchanged for billions of years.

(B) This choice states that terrestrial climate activity i.e. global level of thunderstorms increases and decreases corresponding to the present 11-year solar cycle. This does not prone that the same 11 year solar cycle has continued for billions of years. Terrestrial climate has an uncertain relationship to solar activity.

(C) Whether cyclical climate changes occurred at intervals of longer that 200 years or not, does not in any way strengthen that the solar activity has continued in undisturbed cycles for billions of years.

(D) What happened during one century, or variations in solar cycle activity does not strengthen the model that says solar activity has remained unchanged for billions of years. It is fact contradicts the model.

(E) If the present day periodicity of solar activity, roughly on 11 year cycle is the same cycle that occurred hundreds of millions of years ago, and if the model predicts a self sustaining magnetic field that regulates solar activity with no change then this fact supports the solar activity model which states that the sunspot activity has remained unchanged over billions of years.

The correct answer is option E.

Percent correctly answered: 64.