Insolation & Heat Budget – NDA Geography PYQs

Question 1 [NDA 2006-II]
Which one of the following experiences the least annual range of temperature?
(a) Equator
(b) Tropic of Cancer
(c) Tropic of Capricorn
(d) Arctic Circle

Answer: (a) Equator
The equator receives high and consistent solar radiation throughout the year. The Sun is always relatively high in the sky and day length barely changes. Temperature at the equator is consistently high with very little variation between months — giving the minimum annual range. Annual range increases progressively as you move toward the poles.

---

Question 2 [NDA 2007-II]
The Earth’s reflectivity of solar radiation (albedo) is highest in which one of the following?
(a) Cropland
(b) Forest area
(c) Sand desert
(d) Snow area

Answer: (d) Snow area
Fresh snow reflects 80–90% of incoming sunlight — the highest albedo of any natural surface. This is why snow-covered regions remain cold even when they receive sunlight — most of the Sun’s energy is reflected away rather than absorbed. Cropland, forest, and sand desert all have progressively lower albedos.

---

Question 3 [NDA 2010-I]
Cloudy nights are warmer than clear nights because of:
(a) Greenhouse effect
(b) Depletion of ozone layer
(c) Insolation
(d) Terrestrial radiation

Answer: (d) Terrestrial radiation
Clouds absorb the long-wave terrestrial radiation emitted by the Earth’s surface and radiate some of it back downward. This keeps the surface from cooling as rapidly as it would on a clear night when radiation escapes freely to space. The process is terrestrial radiation — the surface radiating heat outward — which is then intercepted by clouds.

Question 4 [NDA 2010-I]
As we proceed from equator to poles, the daily range of temperature tends to:
(a) Decrease
(b) Increase
(c) Be constant
(d) Fluctuate

Answer: (b) Increase
At the equator, temperature is consistently warm with little variation between day and night and between seasons. Toward the poles, the contrast between summer and winter — and between day and night in different seasons — becomes much greater. The annual and daily range of temperature increases with latitude.

---

Question 5 [NDA 2011-II]
The intensity of insolation depends on:
(a) Altitude
(b) Nature of terrain
(c) Wind
(d) Latitude

Answer: (d) Latitude
Latitude determines the angle at which sunlight strikes the surface. At the equator, rays are nearly vertical and concentrated on a small area — maximum intensity. At the poles, rays arrive at a very low angle and are spread over a large area — minimum intensity. Latitude is the primary determinant of insolation intensity at the global scale.

Question 6 [NDA 2012-I]
The Earth’s surface receives maximum energy at 12 noon but the maximum temperature never occurs at 12 noon. Which of the following reasons are correct?

1. Transformation of solar energy into heat requires some time.
2. The loss of energy through long-wave radiations from the Earth’s surface exceeds the energy received from the Sun at 4:00 pm.
3. Energy received by the Earth from solar radiations continues to exceed the energy lost by outgoing long-wave radiations from the Earth’s surface up to 4:00 pm.

(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3

Answer: (c) 1 and 3 only
Statement 1 is correct — the surface does not instantly convert solar energy to heat; time is needed. Statement 3 is correct — from noon to approximately 4 PM, incoming solar energy still exceeds outgoing terrestrial energy, so temperature continues to rise. After 4 PM, outgoing exceeds incoming and temperature falls. Statement 2 is phrased incorrectly — the loss exceeds input after 4 PM, not at 4 PM.

---

Question 7 [NDA 2012-II]
The average surface temperature of the Earth’s surface is:
(a) 10°C
(b) 15°C
(c) 8°C
(d) 5°C

Answer: (b) 15°C
The Earth’s average surface temperature is approximately 15°C. This is maintained by the natural greenhouse effect — without which the average temperature would be about –18°C. The 33°C difference is entirely due to greenhouse gases trapping outgoing terrestrial radiation.

Question 8 [NDA 2013-II]
The term albedo implies the:
(a) Capacity to absorb solar radiation
(b) Capacity to modify the path of solar radiation
(c) Proportion of the shortwave solar radiation reflected by a surface
(d) Amount of solar radiation returned to air by a surface

Answer: (c) Proportion of the shortwave solar radiation reflected by a surface
Albedo is precisely defined as the fraction (proportion) of incoming shortwave solar radiation that is reflected by a surface back into space. It is expressed as a percentage. Snow has very high albedo (80–90%) while the ocean has very low albedo (5–10%).

---

Question 9 [NDA 2016-II]
Which of the following statements concerning temperature is/are correct?

1. In winter season, isotherms in Northern Hemisphere are more or less circular on continents.
2. Isotherms are parallel to latitude in Southern Hemisphere in oceans.
3. Minimum temperature during winter is recorded in Northern Canada.

(a) 1 and 3 only
(b) 1 and 3 only
(c) 1, 2 and 3
(d) 2 only

Answer: (d) 2 only
Statement 1 is wrong — in winter, isotherms in the Northern Hemisphere are deflected toward lower latitudes over continents (not circular), because continents cool faster than oceans. Statement 2 is correct — the Southern Hemisphere is mostly ocean, so temperatures are uniform and isotherms run parallel to latitude. Statement 3 is debatable — the coldest winters are in Siberia (Russia), not Northern Canada, though Northern Canada is also extremely cold.

---

Question 10 [NDA 2021-II]
The Earth’s atmosphere is mainly heated by which one of the following?
(a) Short wave solar radiation
(b) Reflected solar radiation
(c) Long wave terrestrial radiation
(d) Scattered solar radiation

Answer: (c) Long wave terrestrial radiation
The atmosphere is heated primarily from below — by the long-wave (infrared) radiation emitted by the Earth’s surface after it has been warmed by the Sun. The Sun’s short-wave radiation passes through the atmosphere relatively easily without heating it much. This is why temperature decreases with altitude in the troposphere — the heat source is at the bottom.

Question 11 [NDA 2024-I]
Which of the following statements regarding air temperature is/are correct?

1. Air temperature is measured at a standard height of 1.2 m (4.0 feet) above the ground surface.
2. The average rate of temperature decrease with height is termed as the environmental temperature lapse rate.

(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

Answer: (c) Both 1 and 2
Both statements are correct. Standard meteorological practice measures air temperature at 1.2 m (4 feet) above the ground to avoid the influence of surface heating. The environmental temperature lapse rate describes the average rate at which temperature decreases with altitude in the troposphere — approximately 6.4°C per kilometre.