Light exists on a spectrum of frequencies extending from gamma rays

Question

﻿Light exists on a spectrum of frequencies extending from gamma rays at the highest frequencies to radio waves at the lowest, though human eyes are sensitive to only a narrow range of frequencies in the middle known as the visible spectrum. The different colors we see correspond to the different frequencies of light within that range. Given that there are so many frequencies of light, one might wonder why our eyes didn't evolve to be sensitive to more frequencies.

Gamma rays from space collide with Earth's atmosphere, which converts some of their energy to heat and creates a distinctive cascade of subatomic particles down toward the ground. However, the rays themselves are entirely absorbed before they can reach Earth's surface. Thus, Earth would appear to be pitch black to eyes that were only sensitive to gamma rays. Similarly, the majority of frequencies of light that are higher or lower than those in the visible spectrum-such as ultraviolet and most infrared frequencies, respectively-are mostly or entirely absorbed by Earth's atmosphere.

One reason we see the frequencies we do is that visible-spectrum light generally passes through our atmosphere without being absorbed or reflected. Another reason is that the Sun, in some respects an average star, emits most of its light at frequencies in the visible spectrum, whereas a hot star emits most of its light at ultraviolet frequencies and a very cool star emits most of its light at infrared frequencies.  Indeed, to remarkably high precision, the human eye is most sensitive to the exact frequency in the yellow part of the spectrum at which the Sun is the brightest.

Even if there are living beings on other planets, it is not likely that they would see mainly at very different frequencies than we do. Virtually all gases that are abundant in the cosmos tend to allow frequencies in the visible spectrum to pass through while absorbing other frequencies, and all but the coolest stars put out much, if not most, of their light in the visible spectrum. If there are living beings on other planets, they probably see at roughly the same frequencies as we do, though there may be occasional exceptions.   1 
﻿ 1. The main purpose of the passage is to

A. present certain facts about the cosmos that indicate probable limits to the frequencies of light that living beings would be able to see
B. explain why certain frequencies of light outside the visible spectrum are not abundant in the cosmos
C. discuss the manner in which various forms of matter are affected by interaction with different frequencies of light
D. describe why average stars tend to emit more light at visible-spectrum frequencies than they do at other frequencies
E. discuss whether the temperature of the closest star to a planet affects the frequencies of light that living beings on that planet could potentially evolve to see

2 
﻿ 2. According to the passage, humans evolved eyes sensitive to a particular part of the spectrum of light in part because

A. Earth's atmosphere filters out most of the light emitted by the Sun
B. that part of the spectrum constitutes the full range of frequencies that can penetrate Earth's atmosphere
C. Earth is primarily composed of materials that do not absorb light in that part of the spectrum
D. the majority of the Sun's light is emitted at frequencies in that part of the spectrum
E. most other frequencies of light are reflected by Earth's atmosphere

3 
 3. ﻿Which of the following most accurately describes the purpose of the highlighted sentence in relation to the passage as a whole?

A. To indicate the author's surprise at the manner in which human eyes have developed in relation to the visible spectrum of light
B. To illustrate that the correspondence between human eyes' sensitivity and the frequencies of light comprising the visible spectrum is not merely coincidental
C. To assert that human eyes are more finely tuned to a particular part of the visible spectrum of light than are those of some other organisms on Earth
D. To explain why the gases that comprise Earth's atmosphere do not absorb the frequencies of light that the Sun emits most abundantly
E. To support the claim that the Sun is an average star with respect to the frequencies of light at which it is brightest

4 
﻿ 4. The reasoning in the final paragraph most strongly implies that the author makes which of the following assumptions?

A. The vast majority of the planets in the cosmos have atmospheres.
B. Living beings that evolve on planets orbiting hot stars are more likely to develop the capacity to see than are living beings that evolve on planets orbiting average-temperature stars.
C. Living beings are most likely to evolve on planets with atmospheres containing gases that are abundant in the cosmos.
D. If living beings evolve on planets orbiting the hottest stars, they will likely develop eyes that are sensitive to gamma rays.
E. The frequencies of light that pass through a planet's atmosphere without being absorbed are the frequencies that the nearest star emits most abundantly.

MartyMurray · Accepted Answer

Explanation for Question 1

﻿ 1. The main purpose of the passage is to

We can bring the main purpose of the passage into focus by considering the important points and structure of the passage.

The passage begins by presenting a general fact about light:  "﻿Light exists on a spectrum of frequencies extending from gamma rays at the highest frequencies to radio waves at the lowest."

It then uses the contrast marker "though" to present a contrasting point about human eyes:  "human eyes are sensitive to only a narrow range of frequencies in the middle known as the visible spectrum."

Then, it finishes the first paragraph by bringing up something that "one might wonder":  "Given that there are so many frequencies of light, one might wonder why our eyes didn't evolve to be sensitive to more frequencies."

Then, the second and third paragraphs explain why "we see the frequencies we do."

Finally, the fourth paragraph explains why even "living beings on other planets" do not likely see at frequencies very different from those at which we see.

With these important points in mind, we can go to the answer choices.

A. present certain facts about the cosmos that indicate probable limits to the frequencies of light that living beings would be able to see

As we discussed above, in the first paragraph, the passage brings up that "one might wonder why our eyes didn't evolve to be sensitive to more frequencies."

Then, in the second, third and fourth paragraphs, it presents facts that explain why not only humans but even beings on other planets would be able to see light of only certain frequencies.

So, as this choice says, the passage presents "certain facts about the cosmos that indicate probable limits to the frequencies of light that living beings would be able to see."

Keep

B. explain why certain frequencies of light outside the visible spectrum are not abundant in the cosmos

The passage does not say that or explain why "certain frequencies of light outside the visible spectrum are not abundant in the cosmos."

In the second paragraph, the passage does indicate that the Sun, "an average star," "emits most of its light at frequencies in the visible spectrum," and in the fourth paragraph, the passage says, "all but the coolest stars put out much, if not most, of their light in the visible spectrum." However, that information does not mean that frequencies of light outside the visible spectrum are not abundant in the cosmos. After all, the fact that something is not the "most" does not mean that it is not abundant.

Also, even if it did mean that, the discussions of the light emitted by the Sun and "all but the coolest stars" are just two small parts of the passage.

Eliminate.

C. discuss the manner in which various forms of matter are affected by interaction with different frequencies of light

The passage says that some forms of matter absorb light, but it does not discuss the manner in which forms of matter are "affected" by light.

Eliminate.

D. describe why average stars tend to emit more light at visible-spectrum frequencies than they do at other frequencies

Scanning the passage for "average stars," we find the following:

the Sun, in some respects an average star, emits most of its light at frequencies in the visible spectrum

We see that, while the passage does mention that the Sun, an average star, emits more light at visible-spectrum frequencies than it does at other frequencies, the passage does not "describe why" the Sun does so.

Also, the discussion of the Sun, an average star, is just a small part of the passage. So, the purpose of the passage as a whole is not to discuss average stars.

Eliminate.

E. discuss whether the temperature of the closest star to a planet affects the frequencies of light that living beings on that planet could potentially evolve to see

The passage says the following about the "temperature" of stars:

a hot star emits most of its light at ultraviolet frequencies and a very cool star emits most of its light at infrared frequencies

and

all but the coolest stars put out much, if not most, of their light in the visible spectrum

We could infer from that information that "the temperature of the closest star to a planet affects the frequencies of light that living beings on that planet could potentially evolve to see."

However, the passage does not discuss that idea and is not structured to support that idea. Rather, it mentions those facts about the temperatures of stars in the context of a larger discussion of the frequencies of light that humans and other beings see.

Eliminate.

The correct answer is (A).

Explanation for Question 2

﻿ 2. According to the passage, humans evolved eyes sensitive to a particular part of the spectrum of light in part because

A. Earth's atmosphere filters out most of the light emitted by the Sun

Scanning the passage for "Earth's atmosphere, we find the following:

Similarly, the majority of frequencies of light that are higher or lower than those in the visible spectrum-such as ultraviolet and most infrared frequencies, respectively-are mostly or entirely absorbed by Earth's atmosphere.

We see that what this choice says and what the passage says seem similar, but there is a key difference:

This choice says that "Earth's atmosphere filters out  most of the light emitted by the Sun ."

The passage says that Earth's atmosphere filters out  most of "the majority of frequencies of light that are higher or lower than those in the visible spectrum ."

Most of "the majority of frequencies of light that are higher or lower than those in the visible spectrum" is not the same as "most of the light emitted by the Sun." After all, it could be that "most of the light emitted by the sun" is in the visible spectrum and therefore not filtered out.

So, this choice is not supported.

Eliminate.

B. that part of the spectrum constitutes the full range of frequencies that can penetrate Earth's atmosphere

The passage says the following about "frequencies that can penetrate Earth's atmosphere":

Similarly, the majority of frequencies of light that are higher or lower than those in the visible spectrum-such as ultraviolet and most infrared frequencies, respectively-are mostly or entirely absorbed by Earth's atmosphere.

We see that the passage says that "the majority" of frequencies not in the visible spectrum "are mostly or entirely absorbed by Earth's atmosphere."

Notice that "the majority" of frequencies not in the visible spectrum is not all those frequencies and that "mostly ... absorbed" means that some light penetrates the atmosphere. Thus, the passage is implying that some frequencies other than visible light get through.

So, contrary to what this choice says, the visible light part of the spectrum does not constitute the full range of frequencies that can penetrate Earth's atmosphere.

Eliminate.

C. Earth is primarily composed of materials that do not absorb light in that part of the spectrum

Scanning the passage for "absorb light," we find the following:

One reason we see the frequencies we do is that visible-spectrum light generally passes through our atmosphere without being absorbed or reflected.

Notice that passage says that Earth's atmosphere does not absorb visible light whereas this choice says that the materials that compose Earth itself, rather than its atmosphere, don't absorb visible light.

Since the materials that Earth is composed of and Earth's atmosphere are two different things, this choice is not supported.

Eliminate.

D. the majority of the Sun's light is emitted at frequencies in that part of the spectrum

Scanning the passage for "the majority of the Sun's light," we find the following:

One reason we see the frequencies we do is .... Another reason is that the Sun ... emits  most of its light  at frequencies in the visible spectrum

We see that the passage says that a reason "we see the frequencies we do" is that "the Sun ... emits most of its light, i.e., "the majority of the Suns light," at frequencies in the visible spectrum, which is the same as what this choice says.

Keep.

E. most other frequencies of light are reflected by Earth's atmosphere

Scanning the passage for "reflected by Earth's atmospheres," we find the following:

One reason we see the frequencies we do is that visible-spectrum light generally passes through our atmosphere without being absorbed or  reflected .

That information doesn't help much, so we can scan for "most other frequencies of light" and find the following:

Similarly,  the majority of frequencies of light that are higher or lower than those in the visible spectrum  ... are mostly or entirely absorbed by Earth's atmosphere.

We see that the passage says that "the majority of" or "most" other frequencies of light are "absorbed by Earth's atmosphere," not 'reflected' as this choice says.

Eliminate.

The correct answer is (D).

Explanation for Question 3

3. ﻿Which of the following most accurately describes the purpose of the highlighted sentence in relation to the passage as a whole?

A. To indicate the author's surprise at the manner in which human eyes have developed in relation to the visible spectrum of light

Nothing the author says indicates "surprise at the manner in which human eyes have developed in relation to the visible spectrum of light." On the contrary, the author appear to believe the it is logical, rather than surprising, that human eyes have developed as they have.

Eliminate.

B. To illustrate that the correspondence between human eyes' sensitivity and the frequencies of light comprising the visible spectrum is not merely coincidental

Rereading the highlighted sentence and the surrounding sentences, we see the following:

Another reason (we see the frequencies we do) is that the Sun ... emits most of its light at frequencies in the visible spectrum ....  Indeed, to remarkably high precision, the human eye is most sensitive to the exact frequency in the yellow part of the spectrum at which the Sun is the brightest. "

We see that the author has used the highlighted sentence to emphasize the point that "Another reason (we see the frequencies we do) is that the Sun ... emits most of its light at frequencies in the visible spectrum," by showing that not only do people see light at frequencies at which the Sun emits most of its light but also people's eyes are most sensitive to the brightest of the Sun's light.

The additional information provided by the highlighted portion does indeed "illustrate that the correspondence between human eyes' sensitivity and the frequencies of light comprising the visible spectrum is not merely coincidental." After all, the fact that human eyes are most sensitive to the part of Sun's light that is brightest tends to indicate that there is a connection between the type of light that the Sun produces and the type of light that humans see.

Keep.

C. To assert that human eyes are more finely tuned to a particular part of the visible spectrum of light than are those of some other organisms on Earth

The passage makes no comparison of human eyes with those of other organisms on Earth.

Eliminate.

D. To explain why the gases that comprise Earth's atmosphere do not absorb the frequencies of light that the Sun emits most abundantly

The fact stated by the highlighted sentence, " Indeed, to remarkably high precision, the human eye is most sensitive to the exact frequency in the yellow part of the spectrum at which the Sun is the brightest, " does not explain anything about why gases do not absorb certain frequencies of light.

Eliminate.

E. To support the claim that the Sun is an average star with respect to the frequencies of light at which it is brightest

Although the highlighted sentence follows the statement that "the Sun, in some respects an average star, emits most of its light at frequencies in the visible spectrum," the highlighted sentence does not support the claim that the Sun is an average star. After all, the fact that " Indeed, to remarkably high precision, the human eye is most sensitive to the exact frequency in the yellow part of the spectrum at which the Sun is the brightest, " does not indicate that, among stars, the Sun is average.

Eliminate.

The correct answer is (B).

Explanation for Question 4

﻿ 4. The reasoning in the final paragraph most strongly implies that the author makes which of the following assumptions?

The author's conclusion in the final paragraph is the following:

If there are living beings on other planets, they probably see at roughly the same frequencies as we do, though there may be occasional exceptions.

The author supports that conclusion with this evidence:

Virtually all gases that are abundant in the cosmos tend to allow frequencies in the visible spectrum to pass through while absorbing other frequencies, and all but the coolest stars put out much, if not most, of their light in the visible spectrum.

The assumption the author makes will be information necessary for the evidence to support the conclusion.

A. The vast majority of the planets in the cosmos have atmospheres.

This choice is a little tricky to eliminate since, for gases around a planet to allow only some frequencies of light to reach the planet, the planet must have an atmosphere.

Notice, however, that the author's argument works even if it's not the case that the vast majority of planets have atmospheres. After all, even if only the planets inhabited by living beings have atmospheres, the argument works.

Eliminate.

B. Living beings that evolve on planets orbiting hot stars are more likely to develop the capacity to see than are living beings that evolve on planets orbiting average-temperature stars.

The author's conclusion is that living beings probably see at roughly the same frequencies as we do, which are the visible frequencies of light emitted by average stars.

So, the argument doesn't require the assumption that living beings that evolve on planets orbiting hot stars, which according to the passage emit mostly ultraviolet light that we do not see, are more likely to develop the capacity to see.

Eliminate.

C. Living beings are most likely to evolve on planets with atmospheres containing gases that are abundant in the cosmos.

The argument uses the evidence that "Virtually all gases that are abundant in the cosmos tend to allow frequencies in the visible spectrum to pass through while absorbing other frequencies," to support the conclusion that "If there are living beings on other planets, they probably see at roughly the same frequencies as we do."

We see that the argument involves the idea that the light that living beings on other planets experience is probably light that "gases that are abundant in the cosmos" allow to pass through.

In order for that to be the case, it must be the case that the atmospheres on the planets on which living beings evolved probably contain those abundant gases. Otherwise, it could be that other frequencies of light would get through the atmospheres and that, therefore, the beings would have evolved to see other frequencies.

So, we see that the author is making the assumption stated by this choice, that living beings are most likely to evolve on planets with atmospheres containing gases that are abundant in the cosmos.

Keep.

D. If living beings evolve on planets orbiting the hottest stars, they will likely develop eyes that are sensitive to gamma rays.

This choice may be a conclusion that follows from what the passage says about the hottest stars, but it certainly isn't necessary for supporting the conclusion that living beings on other planets probably see at roughly the same frequencies as we do, which do not include gamma ray frequencies.

Eliminate.

E. The frequencies of light that pass through a planet's atmosphere without being absorbed are the frequencies that the nearest star emits most abundantly.

This choice is actually in conflict with the author's argument, which is based on the idea that the frequencies of light that reach a planet are those that gases "tend to allow" to pass through, rather than those that "the nearest star emits most abundantly."

Eliminate.

The correct answer is (C).

jm2k5 · Answer

MartyMurray

I have some issues with your reasoning of Question 2 Option B.

visible light does constitute the full range of frequencies that can penetrate Earth's atmosphere. Because "constitute" means "to be a part of" and not "whole of".

So, option B really says that visible light is a part of the full range of frequencies that can penetrate Earth's atmosphere. Which is true according to the passage.

So, the Full Range of frequencies is really Visible Light + Some Other Frequencies (because a majority (not all) gets reflected/absorbed).

I think the real issue with Option B is that if Option B were true, we should have been able to see those other frequencies, which the passage states that we don't.

Thoughts ?

MartyMurray · Answer

"Constitutes" means "to form or make up something" or "to be or be considered."

That other definition, "be (a part) of a whole," that appears on Google seems to me to be erroneous.

"Constitutes the full range" means "makes up the full range."

Given the correct definition of "constitutes," choice (B) doesn't mean what you thought it meant. So, the choice works as I explained that it does.

KarishmaB · Answer

Responding to a pm:

Para 1: Light has frequencies from gamma to infra red. Why can't our eyes see all?
Para 2: Gamma and other non visible spectrum does not reach us
Para 3: Why we see what we see - Only visible spectrum reaches us and Sum emits most in visible spectrum
Para 4: Other beings on other planets are also likely to see visible spectrum only.

Question 1.

1. The main purpose of the passage is to

A. present certain facts about the cosmos that indicate probable limits to the frequencies of light that living beings would be able to see
B. explain why certain frequencies of light outside the visible spectrum are not abundant in the cosmos
C. discuss the manner in which various forms of matter are affected by interaction with different frequencies of light
D. describe why average stars tend to emit more light at visible-spectrum frequencies than they do at other frequencies
E. discuss whether the temperature of the closest star to a planet affects the frequencies of light that living beings on that planet could potentially evolve to see

Option (A) covers all the paragraphs. The passage starts with why we only see the visible spectrum and ends with why others would also likely see only the visible spectrum. Hence it discusses certain facts about the cosmos that indicate probable limits to the frequencies of light that living beings would be able to see.
The whole passage is about what living beings can see and options (B), (C) and (D) do not mention it at all. 
Option (E) focuses on one aspect - whether temperature of a star affects the frequencies living beings can see. But that is just one aspect of our discussion.

Answer (A)

Question 2.

﻿ 2. According to the passage, humans evolved eyes sensitive to a particular part of the spectrum of light in part because

A. Earth's atmosphere filters out most of the light emitted by the Sun
B. that part of the spectrum constitutes the full range of frequencies that can penetrate Earth's atmosphere
C. Earth is primarily composed of materials that do not absorb light in that part of the spectrum
D. the majority of the Sun's light is emitted at frequencies in that part of the spectrum
E. most other frequencies of light are reflected by Earth's atmosphere

Answer would be found in para 2 and 3 which discuss the reasons.

A. Earth's atmosphere filters out most of the light emitted by the Sun

Not correct. We are given that  Sun emits most of its light at frequencies in the visible spectrum (which is not filtered out).

B. that part of the spectrum constitutes the full range of frequencies that can penetrate Earth's atmosphere

Given: 
 the majority of frequencies of light that are higher or lower than those in the visible spectrum-such as ultraviolet and most infrared frequencies, respectively-are mostly or entirely absorbed by Earth's atmosphere.
Hence this option is not correct. The passage says that "majority" of other frequencies are mostly absorbed, not ALL. Hence the visible spectrum is not the FULL range of frequencies that can penetrate Earth's atmosphere.
 
  C. Earth is primarily composed of materials that do not absorb light in that part of the spectrum

Composition of Earth is not discussed. Composition of the atmosphere (what stands between us and the light) is discussed.

D. the majority of the Sun's light is emitted at frequencies in that part of the spectrum

Correct. Given:
 Another reason is that the Sun, in some respects an average star, emits most of its light at frequencies in the visible spectrum.

E. most other frequencies of light are reflected by Earth's atmosphere

Not reflected, absorbed. 
 Given:
Similarly, the majority of frequencies of light that are higher or lower than those in the visible spectrum-such as ultraviolet and most infrared frequencies, respectively-are mostly or entirely absorbed by Earth's atmosphere.

Answer (D)

Question 3.

3. ﻿Which of the following most accurately describes the purpose of the highlighted sentence in relation to the passage as a whole?

A. To indicate the author's surprise at the manner in which human eyes have developed in relation to the visible spectrum of light
B. To illustrate that the correspondence between human eyes' sensitivity and the frequencies of light comprising the visible spectrum is not merely coincidental
C. To assert that human eyes are more finely tuned to a particular part of the visible spectrum of light than are those of some other organisms on Earth
D. To explain why the gases that comprise Earth's atmosphere do not absorb the frequencies of light that the Sun emits most abundantly
E. To support the claim that the Sun is an average star with respect to the frequencies of light at which it is brightest

Given: Another reason is that the Sun, in some respects an average star, emits most of its light at frequencies in the visible spectrum, whereas a hot star emits most of its light at ultraviolet frequencies and a very cool star emits most of its light at infrared frequencies.    Indeed, to remarkably high precision, the human eye is most sensitive to the exact frequency in the yellow part of the spectrum at which the Sun is the brightest.

With the highlighted sentence, the author is establishing the correspondence of the sensitivity of our eyes to a certain frequency with the amount of light the Sun emits at that frequency. The highlighted sentence shows that we are most sensitive to the frequency which is emitted the most (and hence makes the Sun appear brightest).
Hence option (B) works.

Answer (B)

Question 4.

﻿ 4. The reasoning in the final paragraph most strongly implies that the author makes which of the following assumptions?

A. The vast majority of the planets in the cosmos have atmospheres.
B. Living beings that evolve on planets orbiting hot stars are more likely to develop the capacity to see than are living beings that evolve on planets orbiting average-temperature stars.
C. Living beings are most likely to evolve on planets with atmospheres containing gases that are abundant in the cosmos.
D. If living beings evolve on planets orbiting the hottest stars, they will likely develop eyes that are sensitive to gamma rays.
E. The frequencies of light that pass through a planet's atmosphere without being absorbed are the frequencies that the nearest star emits most abundantly.

Given: 
 Virtually all gases that are abundant in the cosmos tend to allow frequencies in the visible spectrum to pass through while absorbing other frequencies, and all but the coolest stars put out much, if not most, of their light in the visible spectrum. If there are living beings on other planets, they probably see at roughly the same frequencies as we do, though there may be occasional exceptions.

The author concludes that beings on other planets  probably see at roughly the same frequencies as we do b ased on the characteristics of the gases that are abundant in the cosmos. So she assumes that the atmospheres of planets where living beings have evolved are likely to contain gases that are abundant in the cosmos. Hence option (C) makes sense.

Note that option (A) is incorrect because the author does not conclude about the vast majority of planets. She concludes only about the planets with living beings.

Answer (C)

VerbalBot · Answer

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Light exists on a spectrum of frequencies extending from gamma rays

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Light exists on a spectrum of frequencies extending from gamma rays

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