Absorption and Scattering of Light

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Absorption and Scattering of Light

This lesson aligns with NGSS PS4.B

Introduction

Have you ever wondered why a red apple appears red or why the color of your favorite T-shirt doesn't fade away over time? The answers to these questions lie in a fascinating phenomenon called light absorption. You might have noticed that when you use a flashlight, items that are closer to you seem brighter than objects that are located at a distance. The light appears to weaken as it travels farther away from the flashlight. This occurrence is partially because the beam spreads out and partially because of absorption and scattering. In this article, we will learn about light absorption, uncovering the secrets behind colors, energy transformations, and scattering of light.

Absorption of Light

The process of transferring energy conveyed by light waves to the particles of matter is termed absorption. For instance, when you direct a flashlight into the air, the particles within the air absorb a portion of the energy carried by the light. This outcome causes the light to become dim, as shown in the figure. The farther the light travels away from the flashlight, the more it is absorbed by the particles present in the air.

How Colors Come to Life

When light encounters an object, whether it's a piece of clothing, a fruit, or a painted surface, a remarkable process takes place. Imagine you have a blue shirt. The color you see is not actually "blue" in the shirt's molecules. Instead, the shirt absorbs certain colors from the white light and reflects the color that we see as blue.

Each color we see corresponds to the wavelengths of light that an object absorbs and reflects. A red apple appears red because it absorbs all colors of light except red. The red light is reflected, reaching our eyes and creating the impression of a red apple. This interaction between light and matter is what brings a vibrant array of colors into our lives.

Energy Transformation

As light is absorbed by an object, its energy is not lost—it's transformed. This transformation typically results in the generation of heat. Have you ever noticed that wearing dark-colored clothes on a sunny day can make you feel warmer? That's because dark colors absorb more light and convert more of its energy into heat. On the other hand, light-colored clothes reflect more light, which help keep you cooler.

This energy transformation is also the reason why asphalt or concrete surfaces can become scorching hot on a sunny day. The dark surface absorbs a significant amount of sunlight, converting it into heat energy.

Scattering of Light

Scattering is the process by which light changes direction and spreads out as it interacts with particles in its path. Think of light as little ping-pong balls that bounce around when they hit obstructions. When light rays meet small particles, like molecules in the air, they get deflected in various directions. This is the concept of scattering.

The Blue-Sky Mystery

Now, let's unravel the mystery of the blue sky. Sunlight, though it appears white to our eyes, is a blend of various colors. Each color has a different wavelength. Blue and violet have the shortest wavelengths, while red has the longest. As sunlight enters Earth's atmosphere, it encounters numerous tiny molecules and particles.

Due to its shorter wavelength, blue light gets scattered in all directions by the oxygen and nitrogen molecules in our atmosphere. This scattered blue light reaches our eyes from every part of the sky, making it appear blue, and this is how scattering makes the sky blue.

But you might wonder, "What about violet? Isn't its wavelength even shorter?" Yes, it is! But our eyes are more sensitive to blue light, and the sunlight contains less violet light to begin with. Moreover, some of the violet light is absorbed by the ozone layer, making blue the dominant color we see.

Summary

The process of transferring energy carried by the light waves to the particles of matter is termed absorption of light.
All materials do not absorb light in the same way, rather it depends on the molecular structure of the materials.
Materials with complex structures tend to absorb a wider range of wavelengths, resulting often in darker colors.
The emission of light energy by the matter’s particles that have absorbed energy is known as scattering.
As this light energy is released, it scatters in all directions.

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