What is color? - Colm Kelleher

Summary

This script explores the concept of color as a property of light waves, explaining how light's frequency translates into the colors we perceive. It uses the analogy of a cork bobbing in the ocean to illustrate the periodic motion and frequency of waves. The script further explains that objects appear colored because they reflect specific frequencies of light while absorbing others, turning them into heat. The visible spectrum ranges from red, the lowest frequency, to purple, the highest, with all other colors in between. White reflects all colors, while black absorbs them, affecting how we experience heat from different colored objects.

Takeaways

• 🌊 Waves exhibit a repetitive or periodic motion, which is a fundamental characteristic of their behavior.
• 🕒 The period of a wave is the time it takes for a wave to complete one full cycle of motion.
• 🔢 Frequency is the number of waves that pass a point in a given second and is inversely related to the period.
• 🟡 Light behaves as a wave and its frequency is perceived by our eyes as color.
• 👀 Our eyes detect different frequencies of light as different colors, with red being the lowest and purple the highest frequency in the visible spectrum.
• 🎨 The color of an object is determined by the frequency of light it reflects more than others, while the rest is absorbed and converted into heat.
• 🟨 Yellow objects, like a pencil, appear yellow because they reflect yellow light more than other colors.
• 🔵 Blue and purple light hitting an object is absorbed if not reflected, contributing to the object's color appearance.
• ⚫ Black objects absorb all frequencies of light, which is why they can feel hot under sunlight.
• ⚪ White objects reflect all colors of light, which is why they appear white.
• 🎽 Wearing dark colors, like a black Metallica t-shirt, can be uncomfortable on a sunny day due to the absorption of all light frequencies and increased heat.

Q & A

What is a key property of life that is often associated with color?

One of the most striking properties about life is that it has color, which is a result of the interaction between light and the objects that reflect or absorb it.

Why is it helpful to think about light as a wave to understand color?

Thinking about light as a wave helps us understand color because color is essentially a measure of the frequency of light waves, which our eyes detect as different colors.

What is the definition of a wave's period?

The period of a wave is the time it takes for the wave to complete one full cycle of its motion, as illustrated by the example of a cork bobbing up and down in the ocean.

How is the frequency of a wave related to its period?

The frequency of a wave is the reciprocal of its period. If a wave has a period of 2 seconds, its frequency is 0.5 waves per second, indicating how many waves pass by in one second.

What is the relationship between the frequency of light and color?

The frequency of light determines its color. Different frequencies correspond to different colors that we perceive in the visible spectrum, with red being the lowest frequency and purple the highest.

Why does a yellow pencil appear yellow when placed under sunlight?

A yellow pencil appears yellow because it reflects yellow light more than it reflects other colors. The other colors of light hitting the pencil are absorbed and converted into heat.

What happens to the light that is not reflected by an object?

The light that is not reflected by an object is absorbed, and the energy it carries is transformed into heat.

Why do white objects appear white?

White objects appear white because they reflect all colors of light, not absorbing any particular frequency, which results in the perception of white.

What is the reason black objects are uncomfortable to wear on a sunny day?

Black objects absorb all frequencies of light and convert the energy into heat, making them hotter and thus uncomfortable to wear in direct sunlight.

How does the visible spectrum relate to the colors we see?

The visible spectrum is a continuous band of colors that our eyes can detect, ranging from the lowest frequency (red) to the highest frequency (purple).

What is the significance of the example of the bobbing cork in explaining wave motion?

The bobbing cork serves as a simple and relatable example to illustrate the concept of periodic motion, which is fundamental to understanding how waves, including light waves, behave.

Outlines

00:00

🌈 Understanding Color Through Light Waves

This paragraph introduces the concept of color as a property of light, explained through the analogy of waves. It describes the periodic motion of waves using the example of a cork bobbing on the ocean, and explains the concepts of period and frequency. The paragraph then relates these concepts to light, stating that color is essentially the frequency of light waves detected by our eyes. It also explains how objects appear colored based on the light they reflect, with yellow objects reflecting yellow light and absorbing other colors, turning them into heat. The paragraph concludes with a humorous note on why wearing a black t-shirt on a sunny day can be uncomfortable due to its heat-absorbing properties.

Keywords

💡Color

Color is a visual characteristic of objects resulting from the light they reflect or emit. In the video, color is described as a measure of the frequency of light waves, which is central to understanding the theme of how we perceive the world around us. The script explains that the frequency of light waves determines the color we see, with red being the lowest frequency and purple the highest, forming the visible spectrum.

💡Light

Light is a form of electromagnetic radiation that is visible to the human eye and is essential for vision. The script discusses light as a wave, emphasizing its frequency, which is directly related to color. It explains that the sun emits all colors of light, and objects appear colored based on the light they reflect, such as a yellow pencil reflecting more yellow light.

💡Wave

A wave is a disturbance that transfers energy through space and matter, often characterized by its periodic motion. The video uses the analogy of a cork bobbing on the ocean to illustrate the concept of waves, explaining how the periodic motion of the cork represents the periodic nature of waves and their measurable properties like period and frequency.

💡Period

The period of a wave is the time it takes for a wave to complete one full cycle of motion. In the script, the period is exemplified by measuring the time for a cork to go from its highest to lowest position and back to the highest again, which is found to be two seconds in the example given.

💡Frequency

Frequency is the number of complete wave cycles that pass a point in a given time, typically measured in cycles per second or Hertz (Hz). The video script explains frequency in the context of waves and light, stating that a lower frequency corresponds to a longer period and vice versa, with light frequency directly correlating to color perception.

💡Visible Spectrum

The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye, ranging from red (lowest frequency) to purple (highest frequency). The script describes the visible spectrum as a continuous band of colors that we can see, highlighting how different frequencies of light are perceived as different colors.

💡Reflection

Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. In the context of the video, reflection is used to explain why objects appear colored; they reflect certain colors of light more than others, such as a yellow pencil reflecting more yellow light.

💡Absorption

Absorption is the process by which the energy of a wave is taken up by the material it encounters. The script mentions absorption in relation to light, explaining that objects can absorb light of certain frequencies, converting the energy into heat, which is why black objects absorb all frequencies and can become uncomfortable to wear in the sun.

💡Electromagnetic Radiation

Electromagnetic radiation is a form of energy that travels through space in the form of waves, including visible light, radio waves, microwaves, and X-rays. The script touches on this concept by discussing light as a type of electromagnetic radiation, which has different frequencies and is part of the broader spectrum of waves.

💡Bobbing Cork

The bobbing cork is a metaphor used in the script to illustrate the concept of waves and their properties, such as period and frequency. It serves as a simple, relatable example to help viewers understand the repetitive motion and periodic nature of waves, which is foundational to the discussion of light and color.

💡Heat

Heat is a form of energy that is transferred between objects with different temperatures. In the script, heat is mentioned in the context of light absorption, where the energy of absorbed light is converted into heat, affecting the temperature of an object, such as a black t-shirt becoming hot in the sun.

Highlights

Life has color, a striking property, which can be understood by considering light as a wave.

Waves exhibit periodic motion, as demonstrated by a cork bobbing up and down in the ocean.

The period of a wave is the time it takes to complete one full cycle of motion.

Wave frequency is the number of waves passing by in one second, calculated from the period.

Light, being a wave, has a frequency that our eyes perceive as color.

Color is a measure of the frequency of light waves, with red being the lowest and purple the highest frequency in the visible spectrum.

The frequency of visible light is so high that we cannot see it as a wave, but we can perceive it through color.

Objects appear colored because they reflect light of specific frequencies more than others.

A yellow pencil looks yellow because it reflects yellow light more than other colors, absorbing the rest.

Absorbed light is converted into heat, which is why wearing a black t-shirt on a sunny day can be uncomfortable.

White objects reflect all colors of light, while black objects absorb all frequencies.

The visible spectrum is a continuous band of colors formed by the different frequencies of light.

The sun emits all colors of light, which interact differently with objects based on their color.

Blue objects reflect blue light, and red objects reflect red light, with the rest being absorbed.

Understanding the interaction of light and color helps explain why certain colors are warmer or cooler to wear.

The phenomenon of color in life is a result of the complex interaction between light waves and objects.

Transcripts

One of the most striking properties about life is that it has color.

To understand the phenomenon of color, it helps to think about light as a wave.

But, before we get to that,

let's talk a little bit about waves in general.

Imagine you're sitting on a boat on the ocean watching a cork bob up and down in the water.

The first thing you notice about the motion is that it repeats itself.

The cork traces the same path over and over again... up and down, up and down.

This repetitive or periodic motion is characteristic of waves.

Then you notice something else...

using a stopwatch, you measure the time it takes for the piece of cork

to go over its highest position down to its lowest and then back up again.

Suppose this takes two seconds.

To use the physics jargon, you've measured the period of the waves that cork is bobbing on.

That is, how long it takes a wave to go through its full range of motion once.

The same information can be expressed in a different way by calculating the wave's frequency.

Frequency, as the name suggest, tells you how frequent the waves are.

That is, how many of them go by in one second.

If you know how many seconds one full wave takes,

then it's easy to work out how many waves go by in one second.

In this case, since each wave takes 2 seconds, the frequency is 0.5 waves per second.

So enough about bobbing corks... What about light and color?

If light is a wave, then it must have a frequency. Right?

Well... yes, it does.

And it turns out that we already have a name for the frequency of the light that our eyes detect.

It's called color.

That's right. Color is nothing more than a measure of how quickly the light waves are waving.

If our eyes were quick enough, we might be able to observe this periodic motion directly,

like we can with the cork and the ocean.

But the frequency of the light we see is so high,

it waves up and down about 400 million million times a second,

that we can't possibly see it as a wave. But we can tell, by looking at its color, what its frequency is.

The lowest frequency light that we can see is red and the highest frequency is purple.

In between all the other frequencies form a continuous band of color, called the visible spectrum.

So, what if you had a yellow pencil sitting on your desk?

Well, the sun emits all colors of light, so light of all colors is hitting your pencil.

The pencil looks yellow because it reflects yellow light more than it reflects the other colors.

What happens to the blue, purple and red light?

They get absorbed and the energy they are carrying is turned into heat.

It is similar with objects of other colors.

Blue things reflect blue light, red things reflect red light and so on.

White objects reflect all colors of light,

while black things do exactly the opposite and absorb at all frequencies.

This - by the way - is why it's uncomfortable to wear your favorite Metallica t-shirt on a sunny day.