Question

What happens to light when it is absorbed? When it is emitted? Give an example of each of these phenomena,.

Short answer

Absorbed light transfers energy to materials; emitted light is released energy. Examples: black clothing absorbs light; fluorescent bulbs emit light.

Step-by-step solution

Understanding Absorption

When light is absorbed by a material, its energy is transferred to the material, often increasing the vibration or movement of atoms or molecules within it. This process can lead to an increase in the material's temperature or can be used in chemical reactions, as when plants absorb sunlight for photosynthesis. For example, when black clothing absorbs sunlight, it typically feels warmer than other colors because more light energy is absorbed.

Understanding Emission

Emission occurs when a material releases energy in the form of light. This can happen when excited electrons within atoms or molecules return to lower energy levels, releasing excess energy as photons of light. An example of this phenomenon is seen in fluorescent light bulbs, where an electric current excites gas atoms and the resultant energy emission is visible as light.

Key concepts

Absorption of Light

When light is absorbed by a material, it is not merely vanishing; it is transforming into other forms of energy. As light waves hit an object, they transfer their energy to the particles of that object. This usually results in an increase in vibrational or kinetic energy, making atoms or molecules move or vibrate faster.
For instance, when the sun shines on a black T-shirt, the shirt becomes warmer. This warmth is due to the fabric absorbing the light energy and converting it into heat.

• The absorption of light can increase the temperature of the object.
• It can initiate chemical reactions, such as photosynthesis in plants.

Photosynthesis is a perfect example where light absorption is crucial—plants absorb sunlight to convert it into chemical energy, fueling plant growth and development.

Emission of Light

Light emission occurs when an object releases energy it previously absorbed, usually after that energy excites atoms or molecules, pushing their electrons to higher energy levels. When these electrons fall back to lower levels, they release energy in the form of light.
This process is a key aspect of how many light sources work, such as fluorescent bulbs. In these bulbs, an electric current excites the gas inside, leading to the emission of visible light.

• Emission can occur naturally, as seen in stars, where nuclear reactions produce light.
• Artificial light sources like LEDs also rely on electron movement across energy levels to emit light.

The released light can vary in color, intensity, and form, depending on how energy levels are structured in the emitting substance.

Photosynthesis

Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods with the help of chlorophyll. This involves absorbing light, primarily from the sun, and using this energy to convert carbon dioxide and water into glucose and oxygen.
The process can be summarized in the equation: \[ 6CO_2 + 6H_2O + light ightarrow C_6H_{12}O_6 + 6O_2 \]
Photosynthesis serves a vital role in the ecosystem as it is a primary source of organic matter for nearly all organisms.

• During daylight, plants absorb light energy using chlorophyll.
• This energy initiates chemical reactions, producing glucose, which plants use for growth and energy.

The oxygen by-product is crucial for the survival of aerobic living beings, contributing to the breathable atmosphere.

Electromagnetic Spectrum

The electromagnetic spectrum encompasses all types of electromagnetic radiation, arranged according to their wavelength or frequency. It includes diverse types like gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves, and radio waves.
Visible light, the small part of the spectrum that human eyes can perceive, ranges from violet, with the shortest wavelength, to red, with the longest.

• Each type of electromagnetic radiation has a different range of wavelengths and frequencies.
• Higher energy waves like gamma rays have short wavelengths, while lower energy waves like radio waves have long wavelengths.

Understanding the electromagnetic spectrum helps explain how different technologies (like X-rays) operate and how light absorption and emission can occur across various forms of radiation.