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GS Paper IUPSC Prelims 2019
Climatology & Atmosphere
Question No. 30Interactive Test Mode
00:00
+2-0.66

Q30. Why are dewdrops not formed on a cloudy night?

Why are dewdrops not formed on a cloudy night?

Select the correct option below (or cross out options to eliminate)
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Official Answer Key & Detailed Solution

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Official UPSC Answer KeyUPSC Prelims 2019 • Geography

Correct Answer: Option (B) — Clouds reflect back the Earth’s radiation.

Concept & Option Breakdown

Standard Reference Verified

Option (b) is correct: Dew forms on clear, calm nights when the Earth's surface undergoes rapid radiative cooling, cooling nearby air below its dew point. On cloudy nights, clouds absorb and radiate/reflect back longwave terrestrial radiation, preventing the surface from cooling sufficiently for condensation to occur.

Elimination Heuristic & Exam Approach

Dew formation requires the ground to cool down below the dew point. Clouds act as an insulating blanket reradiating terrestrial heat back to the surface.

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Question Specifications & Syllabus Mapping

Examination & YearUPSC Civil Services Preliminary Examination 2019 (Q30)
Paper & Marking SchemeGS Paper I • 2 Marks (-0.66 Negative for incorrect response)
Syllabus Subject & TopicGeography → Climatology & Atmosphere
Official Answer KeyOption (B) — Clouds reflect back the Earth’s radiation.

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Frequently Asked Questions — UPSC Prelims 2019 Q30

What is the official answer for UPSC Prelims 2019 GS Paper I Question 30 (Geography)?

The official UPSC answer key for this 2019 Geography (Climatology & Atmosphere) question is Option (B): "Clouds reflect back the Earth’s radiation.". Correct attempts carry 2 Marks with -0.66 Negative penalty for wrong answers.

Which UPSC Prelims syllabus topic does this 2019 question belong to?

This question belongs to GS Paper I under the subject "Geography" and micro-topic "Climatology & Atmosphere". You can explore all repeated questions from Climatology & Atmosphere in Acme AI's 3D Prelims PYQ Realm or practice 50 full-length and sectional tests in the APT Prelims Test Series.

How can I solve this Climatology & Atmosphere UPSC Prelims question using option elimination?

Dew formation requires the ground to cool down below the dew point. Clouds act as an insulating blanket reradiating terrestrial heat back to the surface.

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