NCERT Class 11 Geography — Chapter 2: Solar radiation, heat balance and temperature

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Why do the slant rays of the sun pass through a greater depth of the atmosphere than vertical rays?

Official previous-year question

Verified 1 Aug 2026.

Options

ABecause vertical rays are absorbed by the ozone layer.
BBecause the atmosphere is thicker at the poles.
CBecause slant rays travel faster.
DBecause of the angle of inclination.

Did you get this right?

Solution

The correct option is Because of the angle of inclination..

Explanation

The amount of solar radiation (insolation) reaching the Earth's surface is significantly influenced by the angle at which the sun's rays strike the ground. This angle determines both the surface area over which the energy is distributed and the distance the rays must travel through the atmosphere.

Analysis of the Phenomenon:

Angle of Inclination: The primary reason slant rays pass through a greater depth of the atmosphere is the angle of inclination. When solar rays are vertical (perpendicular to the surface), they travel the shortest possible distance through the atmospheric layers.
Geometric Path Length: As the angle of the sun decreases (becoming more oblique or slanted), the path of the rays through the atmosphere becomes longer geometrically. This is similar to crossing a street diagonally versus crossing it straight across; the diagonal path is longer.
Consequences: Because slant rays travel through a greater depth of the atmosphere, they are subject to more scattering, diffusion, and absorption by atmospheric constituents (such as water vapor, dust particles, and ozone) compared to vertical rays. This results in less intense energy reaching the surface at higher latitudes.

Evaluation of Incorrect Options:

Because the atmosphere is thicker at the poles.: This is incorrect because the atmosphere (specifically the troposphere) is actually thinner at the poles (approx. 8 km) compared to the equator (approx. 18 km). Furthermore, the increased path length is a result of the angle of entry, not the static thickness of the atmosphere.
Because slant rays travel faster.: The speed of light is constant within a specific medium; the angle of the rays does not change their speed.
Because vertical rays are absorbed by the ozone layer.: While ozone absorbs UV radiation, this absorption is a process that happens during transmission. It is not the reason why the physical path length is longer.

Key Takeaway:
The angle of inclination dictates the distance solar radiation travels through the atmosphere. Slant rays traverse a longer atmospheric path than vertical rays, leading to greater energy loss before reaching the Earth's surface.

Your note

More from Chapter 2: Solar radiation, heat balance and temperature

Which of the following best explains why the annual insolation received on 3rd January is slightly more than on 4th July?

easy

Consider the following data regarding the Heat Budget of the Earth: 1. 35 units are reflected back from the top of the clouds. 2. 14 units are absorbed within the atmosphere. 3. 51 units are absorbed by the earth’s surface. Which of the statements given above is/are correct?

hard

With reference to the heating of the atmosphere, consider the following statements: 1. Conduction is the process where heat is transferred through horizontal movement of air. 2. Convection is the process of vertical heating of the atmosphere. 3. Advection has no role in the diurnal variation of daily weather in middle latitudes. Which of the statements given above is/are correct?

medium

With reference to the variability of insolation at the surface of the Earth, consider the following statements: 1. The Earth receives slightly more annual insolation on 3rd January than on 4th July. 2. The variation in solar output due to the Earth's distance from the Sun has a drastic effect on daily weather changes. 3. The rotation of the Earth on its axis is one of the factors causing variations in insolation. Which of the statements given above is/are correct?

medium

Which of the following factors is/are responsible for the variations in insolation received at the surface of the Earth? 1. The angle of inclination of the sun’s rays 2. The transparency of the atmosphere 3. The configuration of land in terms of its aspect 4. The revolution of the Earth around the Sun has no influence on insolation variations Select the correct answer using the code given below:

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The correct option is Because of the angle of inclination..

Explanation

Analysis of the Phenomenon:

Angle of Inclination: The primary reason slant rays pass through a greater depth of the atmosphere is the angle of inclination. When solar rays are vertical (perpendicular to the surface), they travel the shortest possible distance through the atmospheric layers.
Geometric Path Length: As the angle of the sun decreases (becoming more oblique or slanted), the path of the rays through the atmosphere becomes longer geometrically. This is similar to crossing a street diagonally versus crossing it straight across; the diagonal path is longer.
Consequences: Because slant rays travel through a greater depth of the atmosphere, they are subject to more scattering, diffusion, and absorption by atmospheric constituents (such as water vapor, dust particles, and ozone) compared to vertical rays. This results in less intense energy reaching the surface at higher latitudes.

Evaluation of Incorrect Options:

Because the atmosphere is thicker at the poles.: This is incorrect because the atmosphere (specifically the troposphere) is actually thinner at the poles (approx. 8 km) compared to the equator (approx. 18 km). Furthermore, the increased path length is a result of the angle of entry, not the static thickness of the atmosphere.
Because slant rays travel faster.: The speed of light is constant within a specific medium; the angle of the rays does not change their speed.
Because vertical rays are absorbed by the ozone layer.: While ozone absorbs UV radiation, this absorption is a process that happens during transmission. It is not the reason why the physical path length is longer.