New NCERT class 11 Geography Chapter-8: Solar Radiation, Heat Balance and Temperature Solutions Pdf

Welcome to the dedicated portal for Class 11 Geography Chapter-8: Solar Radiation, Heat Balance and Temperature Solutions. Mastering textbook exercises is key to scoring high in geography examinations. This resource provides fully solved NCERT questions, including short 30-word answers, detailed 150-word explanations, and practical observatory project guides. From insolation variability to Earth’s heat budget and atmospheric heating processes, these accurate solutions clear all core concepts and making revision seamless.

Multiple choice questions.

(i) The sun is directly overhead at noon on 21st June at:

(a) The equator

(c) 23.5° N

(b) 23.5° S

(d) 66.5° N

• Answer: (c) 23.5° N (Tropic of Cancer during the summer solstice)

(ii) In which one of the following cities, are the days the longest?

(a) Tiruvanantpuram

(c) Hyderabad

(b) Chandigarh

(d) Nagpur

• Answer: (b) Chandigarh (During northern hemisphere summer, day length increases as you move higher in latitude northward)

(iii) The atmosphere is mainly heated by the:

(a) Short wave solar radiation

(c) Long wave terrestrial radiation

(b) Reflected solar radiation

(d) Scattered solar radiation

• Answer: (c) Long wave terrestrial radiation (Atmospheric gases like $CO_2$ absorb longwave radiation emitted from the Earth’s surface)

(iv) Make correct pairs from the following two columns.

Column I	Column II
(i) Insolation	(c) The incoming solar radiation
(ii) Albedo	(d) The percentage of visible light reflected by an object
(iii) Isotherm	(b) The lines joining the places of equal temperature
(iv) Annual range	(a) The difference between the mean temperature of the warmest and the coldest months

• Answer: (i) – (c), (ii) – (d), (iii) – (b), (iv) – (a)

(v) The main reason that the earth experiences highest temperatures in the subtropics in the northern hemisphere rather than at the equator is:

(a) Subtropical areas tend to have less cloud cover than equatorial areas.

(b) Subtropical areas have longer day hours in the summer than the equatorial.

(c) Subtropical areas have an enhanced “green house effect” compared to equatorial areas.

(d) Subtropical areas are nearer to the oceanic areas than the equatorial locations.

• Answer: (a) Subtropical areas tend to have less cloud cover than equatorial areas. (Clear skies allow maximum insolation to reach the surface, whereas equatorial regions face daily cloudiness)

Answer the following questions in about 30 words.

(i) How does the unequal distribution of heat over the planet earth in space and time cause variations in weather and climate?

Unequal heating creates temperature gradients, causing atmospheric pressure differences. Winds and ocean currents transfer heat from surplus tropical zones to deficit polar regions, driving global weather patterns and climate variations.

(ii) What are the factors that control temperature distribution on the surface of the earth?

The main controlling factors are:

• Latitude (angle of solar rays)
• Altitude (elevation above sea level)
• Distance from the sea (maritime vs. continental effect)
• Air-mass circulation and ocean currents
• Local topographic aspect

(iii) In India, why is the day temperature maximum in May and why not after the summer solstice?

In May, clear skies and overhead sun bring peak insolation. By late June (after the solstice), the arrival of the southwest monsoon brings cloud cover and rainfall, cooling surface temperatures.

(iv) Why is the annual range of temperature high in the Siberian plains?

Extreme continentality, far distance from oceanic moderating influences, high latitude, and extensive snow cover cause rapid summer heating and intense winter cooling, producing a massive temperature range exceeding 60° C.

Answer the following questions in about 150 words.

(i) How do the latitude and the tilt in the axis of rotation of the earth affect the amount of radiation received at the earth’s surface?

The axial tilt ( 66½° to the orbital plane) and latitude together determine the angle of incidence of sun rays and day length.

• Latitude and Inclination Angle: Near the equator, sun rays fall nearly vertically, concentrating energy over a smaller surface area. Moving toward higher latitudes, the sun’s angle becomes slant. Slant rays spread solar energy over a larger area and pass through a thicker atmospheric layer, resulting in greater absorption, scattering, and loss of heat.
• Axial Tilt and Day Length: The inclination of Earth’s axis causes seasonal shifts in day length across latitudes. During summer, longer daylight hours allow continuous solar energy absorption. In winter, shorter days reduce daily insolation, creating extreme thermal variations between equatorial, mid-latitude, and polar regions.

(ii) Discuss the processes through which the earth-atmosphere system maintains heat balance.

Earth maintains its heat balance (heat budget) by returning an equal amount of energy back to space for the 100 units of shortwave insolation it receives.

Incoming Solar Energy (100 Units) ──> Reflected Albedo (35 Units) + Absorbed (65 Units)
Absorbed Heat (51 Earth + 14 Atmosphere) ──> Radiated Outward ──> 65 Units to Space

• Albedo (35 Units): Reflected directly back to space before heating Earth—27 units from cloud tops, 6 units scattered by air, and 2 units from snow and ice cover.
• Surface Absorption and Radiation (51 Units): The Earth absorbs 51 units. It radiates 17 units directly to space as longwave terrestrial radiation and transfers 34 units to the atmosphere through conduction, convection/turbulence (9 units), and latent heat of condensation (19 units).
• Atmospheric Balance: The atmosphere absorbs 48 units (14 from incoming insolation + 34 from terrestrial radiation) and radiates them back to space. Total outgoing radiation (35 + 17 + 48 = 100 units) ensures constant global temperatures.

(iii) Compare the global distribution of temperature in January over the northern and the southern hemisphere of the earth.

January temperature distribution reveals stark contrasts between hemispheres due to differential land-sea distribution and seasonal opposition.

Feature	Northern Hemisphere (Winter)	Southern Hemisphere (Summer)
Dominant Surface	Vast landmasses cause extreme thermal variations.	Dominant ocean coverage maintains gradual changes.
Isotherm Pattern	Irregular, highly bent isotherms; severe deviance over land and water.	Smooth, regular isotherms running nearly parallel to latitudes.
Ocean vs. Land Bending	Isotherms bend northward over oceans (warm Gulf Stream) and southward over land (Siberia).	Isotherms show minimal bending across narrow landmasses.
Temperature Ranges	Extreme cold interiors (e.g., Siberian plain drops to -48°C).	Mild summer baselines (e.g., 20°C along 35°S, 10°C along 45°S.

Project Work

Select a meteorological observatory located in your city or near your town. Tabulate

the temperature data as given in the climatological table of observatories :

(i) Note the altitude, latitude of the observatory and the period for which the mean is calculated.

(ii) Define the terms related to temperature as given in the table.

(iii) Calculate the daily mean monthly temperature. 

Meteorological Observatory Report: Safdarjung Observatory (Delhi)

(i) Observatory Location Details & Baseline Data

Metric	Details
Observatory Name	Safdarjung Observatory (IMD Station ID: 42182)
Location / Region	New Delhi, India
Latitude	28° 35′ N
Longitude	77° 12′ E
Altitude (Elevation)	216 meters above mean sea level
Climatological Reference Period	1981–2010 (Standard 30-year IMD Climatological Base)

(ii) Definitions of Climatological Temperature Terms

• Mean Daily Maximum Temperature: The average of the highest temperatures recorded during every 24-hour period for a given month over the reference period.
• Mean Daily Minimum Temperature: The average of the lowest temperatures recorded during every 24-hour period for a given month over the reference period.
• Daily Mean Monthly Temperature: The arithmetic average of the mean daily maximum and mean daily minimum temperatures for a specific month.
• Highest Recorded Temperature (Extreme): The absolute maximum temperature recorded at the observatory during a specific month across the entire observation period.
• Lowest Recorded Temperature (Extreme): The absolute minimum temperature recorded at the observatory during a specific month across the entire observation period.
• Diurnal Temperature Range: The difference between the maximum and minimum temperatures recorded within a single 24-hour day.

(iii) Calculation of Daily Mean Monthly Temperature

The Daily Mean Monthly Temperature (T_mean) is calculated using the standard climatological formula:

T_mean = (Mean Daily Maximum Temperature + Mean Daily Minimum Temperature) /2

Sample Data Table & Calculation (Safdarjung Observatory, Delhi):

Month	Mean Daily Max (∘C)	Mean Daily Min (∘C)	Calculation Formula	Daily Mean Monthly Temp (∘C)
January	20.5	7.6	(20.5 + 7.6)/2	14.05
February	23.9	10.4	(23.9 + 10.4)/2	17.15
March	29.6	15.6	(29.6 + 15.6)/2	22.60
April	36.3	21.3	(36.3 + 21.3)/2	28.80
May	39.5	25.8	(39.5 + 25.8)/2	32.65
June	39.2	27.9	(39.2 + 27.9)/2	33.55
July	35.3	27.1	(35.3 + 27.1)/2	31.20
August	34.1	26.2	(34.1 + 26.2)/2	30.15
September	34.1	24.6	(34.1 + 24.6)/2	29.35
October	32.8	19.1	(32.8 + 19.1)/2	25.95
November	27.8	12.9	(27.8 + 12.9)/2	20.35
December	22.3	8.3	(22.3 + 8.3)/2	15.30

Key Observations from the Data

1. Thermal Peak: The highest daily mean monthly temperature occurs in June (33.55° C) due to pre-monsoon heating and high insolation.
2. Thermal Minimum: The lowest daily mean monthly temperature occurs in January (14.05°C) during peak winter conditions.
3. Diurnal Variations: Clear sky conditions in pre-monsoon months (April–May) produce wide daily temperature ranges, whereas monsoon cloudiness in July and August narrows the gap between daily maximum and minimum temperatures.