Question map
With reference to the Earth's atmosphere, which one of the following statements is correct?
Explanation
The correct answer is Option 3.
The Earth's atmosphere is transparent to shortwave solar radiation but opaque to longwave terrestrial radiation. Water vapour, concentrated primarily in the troposphere (lower atmosphere), acts as a potent greenhouse gas. It possesses high absorption bands for infrared radiation, trapping heat and maintaining the Earth's thermal balance. This process is crucial for the greenhouse effect.
Other options are incorrect because:
- Option 1: Insolation at the equator is roughly 2.4 times (not 10 times) that at the poles.
- Option 2: Infrared radiation accounts for approximately 45-50% of the total solar spectrum, while visible light accounts for about 40%; thus, it is not two-thirds.
- Option 4: Infrared waves are not part of the visible spectrum; they have longer wavelengths and are located beyond the red end of the visible light range in the electromagnetic spectrum.
PROVENANCE & STUDY PATTERN
Guest previewThis is a classic 'NCERT Fundamental' check, specifically targeting the confusion between Incoming Solar Radiation (Insolation) and Outgoing Terrestrial Radiation. It combines concepts from Chapter 7 (Composition) and Chapter 8 (Heat Budget) of Class XI Physical Geography. The trap lies in mixing up the properties of Shortwave (Solar) and Longwave (Terrestrial) radiation.
This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.
- Statement 1: In the context of Earth's atmosphere, is the total solar insolation received at the equator roughly ten times the insolation received at the poles?
- Statement 2: In the context of Earth's atmosphere, do infrared rays constitute roughly two-thirds of the incoming solar radiation (insolation)?
- Statement 3: In Earth's atmosphere, are infrared waves largely absorbed by atmospheric water vapour?
- Statement 4: In Earth's atmosphere, is atmospheric water vapour concentrated in the lower atmosphere (the troposphere)?
- Statement 5: In the context of Earth's atmosphere and solar radiation, are infrared waves part of the visible spectrum of electromagnetic radiation?
- Explicitly states that total insolation by latitude "does not vary a great deal", which argues against a large (≈10×) difference.
- Notes curvature is important but implies latitudinal differences are moderate rather than an order-of-magnitude.
- States equator gets more intense sunlight but gives a concrete example at 60°N where the sun "heats a given parcel of ground with only a half", implying roughly ~2× differences in intensity at mid-latitudes rather than ~10×.
- Supports the view that differences are substantial but not order-of-magnitude.
- Notes simply that "The amount of insolation decreases from the equator towards the poles," confirming a gradient but giving no support for a 10× factor.
- Provides general confirmation of latitudinal decrease but no large-magnitude claim.
Gives actual measured surface insolation ranges: ~320 W/m² in the tropics and ~70 W/m² in the poles, showing a multi‑fold difference between low and high latitudes.
A student can compare these numbers (320 vs 70 W/m² → ~4.6×) with the claimed 10× ratio to judge that the claim seems larger than the values cited.
States the general geometric rule that energy per unit area decreases from equator to poles because rays are direct at the equator and increasingly oblique toward poles.
Combine this geometric rule with the cosine (angle) effect from basic geometry or a world map to estimate relative insolation at different latitudes and check plausibility of a 10× factor.
Explains that at the equator solar rays are concentrated while near the poles they are spread over a larger area and pass through more atmosphere, both reducing polar insolation.
Use the two effects (area spreading + longer atmospheric path) together with simple trigonometry or known latitude differences to estimate how much weaker polar insolation should be.
Gives the average incoming solar radiation at the top of the atmosphere (1.94 cal/cm²/min ≈ solar constant at TOA), providing a baseline before atmospheric attenuation.
A student can compare TOA values with surface values (from other snippets) to see how atmospheric losses alter latitudinal contrasts and whether a 10× surface ratio is feasible.
Describes latitudinal patterns of net radiation (surplus in tropics, deficit near poles), confirming systematic decrease poleward though not giving exact multipliers.
Use this qualitative pattern plus quantitative surface numbers (snippet 1) to infer that while poles receive markedly less, the difference is on the order of a few times rather than an order of magnitude.
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This statement analysis shows book citations, web sources and indirect clues. The first statement (S1) is open for preview.
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This statement analysis shows book citations, web sources and indirect clues. The first statement (S1) is open for preview.
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This statement analysis shows book citations, web sources and indirect clues. The first statement (S1) is open for preview.
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