UNIT 4: Absorption of Light

Project Number: 2023-1-PL01-KA220-SCH-000164042

UNIT 4: Absorption of Light

Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Education and Culture Executive Agency (EACEA). Neither the European Union nor EACEA can be held responsible for them.

Introduction

In this activity we will focus on the reflection and absorption of light. We will discover how the amount of absorption of light depends on what is happening.

source: freepik.com

Learning Outcomes

Student:

• Concludes that white light is a combination of all light colours.

• Discovers that light can be absorbed by matter as a result of its interaction with matter.

source: freepik.com

• The rainbow that appears on a rainy day when the clouds disperse and the sun begins to shine is a fascinating natural phenomenon that attracts the attention of many people.
• The rainbow, which is the subject of many stories and legends with its beautiful appearance, has led to the emergence of many puzzles and question marks for curious minds.
• For example, what is the relationship between rainbows and rain? Why is the order of colors in the rainbow the same every time?
• Let's take a look at Newton's work on optics to find answers to these questions.

source: freepik.com

• Sir Isaac Newton was the first scientist to correctly explain the nature of light. Until the 1660s, it was believed that white light was a color on its own. In 1666, Newton conducted a prism experiment in a dark room and showed that, contrary to popular belief, white light is actually a mixture of all colors. In this experiment, Newton was actually aiming to explain how rainbows are formed.

• With a simple setup in which sunlight passed through a prism, white light refracted at different angles created an artificial rainbow with red, orange, yellow, green, blue and purple colors on the reflected surface.

source: freepik.com

• So what was going on to create all the known colors when white light passed through the prism?

• Newton could not answer this question because the structure of light was not yet understood at the time.

• About 135 years after Newton's experiment, in 1801, scientist Thomas Young proved that light is a wave. Young proved that as light passes through a prism, it is refracted at different angles according to its wavelength and thus separated into its colors.

source: freepik.com

source: freepik.com

So far we have understood that when white light is refracted, other colors of light are formed. It is also possible to say the opposite. That is, the combination of light colors creates white light. But there is still one more question we need to answer: Why is the order of colors in the rainbow always the same? Let's do a little experiment to find the answer to this question.

LEARNING ACTIVITY:

• On a hot summer day, you may have felt warmer when you wore dark-colored clothes. Wearing light-colored clothes in hot weather can make you feel less affected by the heat.

But how?

• In this activity, we will examine the temperature increase of identical materials of different colors under light. Perform the experiment in an augmented reality environment.

OBSERVATION 1: When you measure the temperature of different coloured T-shirts under sunlight (white light), record the temperature data in the table below. (The T-shirts are made of the same type of fabric).

What do you think is the reason for this difference in temperature values? …………………………………………………………………………………………………………………

OBSERVATION 2: Repeat the experiment this time using different coloured lights.

• When we look at a red T-shirt in sunlight, we see it as red because it reflects only the red colours of the white light falling on it.

• Remember that sunlight (i.e. white light) is a combination of all the colours of light.

• So where have all the other colours of light in sunlight disappeared except red? How do you think this could be related to the heating of the T-shirt in sunlight? Discuss with your peers. .............................……………………………………………………………………................................................………………………………………………………………………………………………………

• Do you think that dark coloured objects always heat up more when they are exposed to sunlight? Is colour the only factor affecting the absorption of light? Discuss with your peers. …………………………………………………………............................………………………………......……………………………………………………………………………………………………………………