Problem 6 - Astronomy Journey to the Cosmic Frontier

Question

A body absorbs \(30 \%\) of the light that strikes it. What is the albedo of the body? What happens to the light striking the body that isn't absorbed?

Step-by-Step Solution

Answer

The albedo of the body is 70%. Light that isn't absorbed is reflected.

Step 1: Understanding Absorption and Albedo

The problem states that a body absorbs 30% of the light that strikes it. In scientific terms, the percentage of light that is reflected by a surface is called its 'albedo'. Albedo is calculated as the percentage of incident light that is reflected.

Step 2: Calculating Albedo

If a body absorbs 30% of the light, this means that it reflects 100% - 30% = 70% of the light. Therefore, the albedo of the body is 70%.

Step 3: Exploring Non-Absorbed Light

The light that isn't absorbed by the body is reflected. Since the body absorbs 30% of the light, the remaining 70% is reflected. This is what contributes to the albedo.

Key Concepts

Light Absorption

When light hits an object, some of it is taken in or absorbed. This process is called light absorption. It means the object is soaking up some of the energy from the light. Not all objects absorb light in the same way. Different surfaces and materials absorb different amounts of light.

• Dark surfaces tend to absorb more light.
• Light surfaces usually absorb less, reflecting more light back.

This absorption happens because the absorbed light gets converted into other forms of energy, like heat. Have you ever noticed how a dark T-shirt feels hotter in the sun compared to a white one? That's because dark colors absorb more sunlight, converting it into heat. The remaining light that is not absorbed is either reflected or transmitted through the material. In our exercise, the body absorbs 30% of the incoming light, contributing to a lower reflection—or albedo—since less light is bounced back.

Reflection of Light

When light hits a surface and bounces back, rather than getting absorbed or passing through, it is called the reflection of light. This phenomenon is crucial in determining the albedo of an object. The smoother and lighter the surface, the more efficiently it can reflect light.

• Reflection helps objects to appear shiny or luminous.
• Highly reflective surfaces, such as mirrors, reflect almost all incoming light.

Reflection is essential in various fields. For example, architects use it to design bright spaces by using materials and colors that reflect more light. Understanding reflection is also vital in making things more energy-efficient, as it impacts how much energy is absorbed as heat. In the context of the exercise, 70% of the light is reflected, as the body does not absorb this portion. This reflection is what contributes to the body's albedo, making it appear brighter.

Incident Light

Incident light is the light that strikes a surface before it is absorbed, reflected, or transmitted. It can be thought of as the initial light energy that a surface receives. Understanding incident light is important when analyzing the behavior of light.

• It is the source of both absorbed and reflected light.
• The intensity and angle of incident light can affect how much is absorbed or reflected.

The concept of incident light helps us to calculate a material's albedo, which is the proportion of the reflected light out of the total light striking the surface. In our exercise scenario, incident light is split between absorbed and reflected portions. The body's albedo (70%) is derived from the incident light that is reflected, not absorbed. Thus, by understanding the role of incident light, we can better predict the behaviors of different materials when exposed to light.