Science Exploration Notes Class 9 English Medium 2026-27

Science Exploration Chapter 13. Earth as a System: Energy, Matter, and Life

CBSE Notes New Syllabus: Class 9

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Chapter 13. Earth as a System: Energy, Matter, and Life

This section explains the Sun as the primary source of energy for the Earth. It describes electromagnetic radiation, the electromagnetic spectrum, solar radiation, insolation and the solar constant, which together explain how energy reaches the Earth and drives natural processes.

Solar Energy and Electromagnetic Radiation

The Sun – Primary Source of Energy

The Sun is the primary source of energy for the Earth. Almost all weather phenomena, climate systems and biological activities depend directly or indirectly on solar energy. It drives the water cycle, wind circulation, ocean currents and photosynthesis. 

Solar Radiation

Solar radiation is the energy emitted by the Sun and transmitted through space in the form of electromagnetic waves. When this energy reaches the Earth, it becomes the main driving force behind Earth's natural systems. 

Electromagnetic Radiation

Electromagnetic radiation is a form of energy that travels through space as waves without requiring any material medium.

Characteristics of Electromagnetic Radiation

• Travels at the speed of light.
• Does not require a medium for propagation.
• Carries energy from the Sun to the Earth.
• Different types differ in wavelength and energy.

Electromagnetic Spectrum

The electromagnetic spectrum is the complete range of electromagnetic radiations arranged according to their wavelength and frequency. 

Solar Radiation Reaching the Earth

Only a part of the Sun's radiation reaches the Earth's surface. During its journey through the atmosphere, some energy is absorbed, reflected or scattered by gases, clouds and dust particles. The remaining energy reaches the surface and supports life. 

Insolation

Insolation (Incoming Solar Radiation) is the amount of solar energy received by the Earth's surface. It is the primary source of energy for weather, climate and biological processes. 

Factors Affecting Insolation

• Latitude.
• Angle of the Sun's rays.
• Duration of sunshine.
• Cloud cover.
• Atmospheric dust and water vapour.
• Season of the year.

Solar Constant

The solar constant is the average amount of solar energy received per unit area at the outer boundary of the Earth's atmosphere when the Sun's rays fall perpendicular to the surface. 

Importance of Solar Energy

• Provides energy for photosynthesis.
• Drives the water cycle.
• Produces winds and ocean currents.
• Maintains Earth's temperature.
• Supports all forms of life.
• Controls weather and climate.

Key Terms at a Glance

Our Concept Builder

Solar energy is the driving force behind almost every natural process on Earth. It reaches the planet through electromagnetic radiation, and the amount of energy received as insolation determines weather patterns, climate, biological productivity and the overall functioning of the Earth System. 

Our Exam Booster

• Remember the definitions of solar radiation, electromagnetic radiation, insolation and solar constant.
• Know the order of the electromagnetic spectrum.
• Understand why only a part of solar radiation reaches the Earth's surface.
• Learn the factors affecting insolation.
• Remember that infrared radiation mainly heats the Earth, while ultraviolet radiation is largely absorbed by the ozone layer.
• CBSE competency-based questions may ask students to explain how solar energy controls weather, climate and life on Earth.