Light exists on a spectrum of frequencies extending from gamma rays at the highest frequencies to radio waves at the...
GMAT Reading Comprehension : (RC) Questions
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.
The main purpose of the passage is to
1. Passage Analysis:
Progressive Passage Analysis
| Text from Passage | Analysis |
|---|---|
| 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. | What it says: Light comes in many different frequencies arranged from highest (gamma rays) to lowest (radio waves), but humans can only see a small portion in the middle. What it does: Sets up the basic framework for the entire passage by establishing the light spectrum and human limitation. Source/Type: Scientific fact Connection to Previous Sentences: This is the opening sentence - establishes the foundation. Visualization: Imagine a piano keyboard with 100 keys, but human eyes can only "see" 10 keys in the middle section. Reading Strategy Insight: This sentence establishes a central limitation that the passage will explore - why are we limited to this narrow range? |
2. Passage Summary:
Human eyes evolved to see visible light frequencies because these are the only frequencies that both pass through Earth's atmosphere and are strongly emitted by our Sun, and these same conditions likely exist throughout the universe.
- The passage establishes universal physical constraints (atmospheric absorption, stellar emission) that limit viable vision frequencies
- Extends reasoning from humans to "living beings on other planets" showing this is about general limits
- Concludes that aliens would "probably see at roughly the same frequencies as we do" based on cosmic facts
- Uses phrases like "virtually all gases that are abundant in the cosmos" to establish universal principles
- The passage doesn't explain why non-visible frequencies are scarce in the cosmos
- Instead, it explains why these frequencies don't reach planetary surfaces due to atmospheric absorption
- The focus is on transmission/absorption, not cosmic abundance of different frequencies
- Too broad - the passage focuses specifically on vision and atmospheric transmission
- Doesn't capture the main purpose of explaining evolutionary limits on vision
- The passage isn't a general survey of light-matter interactions
- Too narrow - this is just one supporting detail, not the main purpose
- The passage mentions average stars briefly to contrast with hot and cool stars
- Doesn't account for the atmospheric absorption component or the broader conclusions about alien vision
- Too narrow - focuses only on temperature effects rather than the broader cosmic constraints
- Misses the atmospheric absorption component which is equally important
- The passage discusses star temperature as one factor among several, not as the main focus