Light | Grade 8 Science DepEd MELC Quarter 1 Module 4 Part 3

Summary

This educational video explores the science of light, including its properties as an electromagnetic wave and its role in creating color. It delves into concepts like refraction, where light bends as it passes through different media, and reflection, which can be either diffused or specular depending on the surface. The script also explains phenomena like rainbows, apparent depth, and the colors of sunsets and the sky, attributing these to light's interaction with water droplets and the Earth's atmosphere. The video concludes with a reminder of the inverse relationship between wavelength and frequency and the direct relationship between frequency and energy.

Takeaways

• 🌈 Light is a transverse wave and an electromagnetic wave, which gives color to our world.
• 🔍 When sunlight hits a mirror under water, it refracts, separating into a spectrum of colors that can form a rainbow on a piece of paper.
• 👀 The human eye can only perceive a narrow band of the electromagnetic spectrum, which we call visible light.
• 🌊 Apparent depth is an optical illusion caused by the refraction of light as it passes from air into water, making objects appear closer to the surface than they really are.
• 🏊‍♂️ Light does not require a medium to travel and moves at its fastest speed in a vacuum, slowing down when it passes through denser media.
• 💡 The speed of light varies depending on the medium it travels through, which causes the bending of light when crossing different media.
• 🪞 Reflection of light can be either diffused, scattering in many directions off rough surfaces, or specular, reflecting in one direction off smooth surfaces like mirrors.
• 🌈 A prism demonstrates dispersion, where white light is split into its constituent colors due to different degrees of refraction for each color.
• 🌅 The colors of the sky and sunsets are explained by Rayleigh scattering, which scatters shorter wavelengths (like blue) more than longer ones (like red).
• ⏳ Wavelength and frequency are inversely proportional, while frequency and energy are directly proportional, affecting the colors we see and the energy of light.

Q & A

What is light and how does it relate to the colors we see?

Light is an electromagnetic wave that exhibits characteristics and properties of a wave. It is responsible for giving color to our world as it is a mixture of visible colors, each with its own frequency and wavelength.

How does the activity with a mirror and water demonstrate the properties of light?

The activity demonstrates that when sunlight shines on a mirror placed under water, the light bends (refracts) and separates into different colors, creating a rainbow on a piece of paper. This shows that light can be dispersed into its constituent colors.

What is the human eye's sensitivity to the electromagnetic spectrum?

The human eye is sensitive to a narrow portion of the electromagnetic spectrum, specifically the visible light that lies between infrared and ultraviolet.

What is apparent depth and how is it related to light refraction?

Apparent depth is an optical illusion where objects under water appear closer to the surface than they actually are. This phenomenon occurs due to the bending of light as it passes from water to air, which is a result of refraction.

How does the speed of light change when it travels through different media?

Light travels at its maximum speed in a vacuum, approximately 3 times 10^8 meters per second. Its speed decreases when it travels through denser media, indicating that the speed of light is dependent on the properties of the medium.

What is the difference between diffused reflection and specular reflection?

Diffused reflection occurs when light strikes a rough, textured, or uneven surface and scatters in many directions, allowing us to see objects from any angle. Specular reflection happens when light hits a smooth, flat, and shiny surface and is reflected in one direction, enabling us to see an image on the surface.

What is dispersion and how is it related to the formation of a rainbow?

Dispersion is the process by which light is separated into its colors due to differences in degrees of refraction. A rainbow is formed by the dispersion of sunlight in water droplets, where light is refracted, dispersed, and internally reflected before emerging and being reflected again at different angles.

Why does the sky appear blue and sunsets appear red?

The sky appears blue due to Rayleigh scattering, where shorter wavelengths like blue are scattered more by the atmosphere. Sunsets appear red because at these times, sunlight travels a longer distance through the atmosphere, and shorter wavelengths like blue are scattered out, leaving the longer wavelengths like red to reach our eyes.

How are wavelength and frequency related to the energy of light?

Wavelength and frequency are inversely proportional, meaning that as the wavelength increases, the frequency decreases. Conversely, frequency and energy are directly proportional, so higher frequencies correspond to higher energy levels.

What is the significance of the speed of light and how does it relate to our perception of thunder and lightning?

Light travels much faster than sound, which is why we see lightning before we hear thunder. The speed of light in a vacuum is approximately 300 million meters per second, which is significantly faster than the speed of sound, allowing us to perceive the light from lightning almost instantaneously compared to the sound of thunder.

Outlines

00:00

🌈 Light and Color: Understanding the Basics

This paragraph introduces the concept of light and color, explaining light as a transverse wave and an electromagnetic wave. It guides viewers through an activity involving a mirror and water to demonstrate the dispersion of light into a spectrum of colors, similar to a rainbow. The activity illustrates how different colors refract at various angles due to their distinct frequencies and wavelengths. The paragraph also touches on the human eye's sensitivity to a narrow spectrum of light and the concept of apparent depth, an optical illusion caused by the refraction of light as it passes from air into water.

05:01

🌞 Exploring Light Phenomena: Refraction, Reflection, and Color Dispersion

The second paragraph delves deeper into the properties of light, such as refraction and reflection. It uses the example of a pencil in water to explain how light bends when it travels from one medium to another with different optical densities. The paragraph discusses the difference between diffused reflection, which occurs on rough surfaces allowing us to see objects from various angles, and specular reflection, which happens on smooth surfaces like mirrors. It also explains the phenomenon of dispersion, using a prism to demonstrate how white light splits into a spectrum of colors. The paragraph concludes with an exploration of why sunsets are red and why the sky is blue, attributing these to the scattering of light in the atmosphere and the different wavelengths of light.

Keywords

💡Light

Light is a form of electromagnetic radiation that is visible to the human eye. It is central to the video's theme as it is the medium through which we perceive color and the world around us. The video explains that light exhibits wave-like properties and is responsible for the colors we see when it interacts with objects and the environment, such as in the activity where sunlight is reflected off a mirror into a rainbow on a piece of paper.

💡Electromagnetic Wave

An electromagnetic wave is a type of wave that can travel through a vacuum and carries electromagnetic force. The video classifies light as an electromagnetic wave, emphasizing its ability to travel without a medium and its behavior when interacting with different media, such as air and water. This concept is crucial for understanding phenomena like refraction and reflection, which are discussed in the script.

💡Refraction

Refraction is the bending of light as it passes from one medium to another with different optical densities. The video uses the example of sunlight entering water and bending, which leads to the separation of light into its constituent colors, creating a rainbow. This phenomenon is key to understanding how different colors of light behave when they encounter various media.

💡Reflection

Reflection is the process by which light bounces back after hitting a surface. The video distinguishes between diffused reflection, which occurs on rough surfaces and allows us to see objects from different angles, and specular reflection, which happens on smooth surfaces like mirrors, creating a clear image. Reflection is integral to how we see our surroundings, including our own image in a mirror.

💡Dispersion

Dispersion is the process by which light is separated into its component colors due to varying degrees of refraction. The video explains that when white light passes through a prism, it splits into a spectrum of colors, demonstrating dispersion. This concept is essential for understanding the formation of rainbows, where sunlight is dispersed by water droplets in the atmosphere.

💡Wavelength

Wavelength is the physical length of a single wave, measured from one peak to the next. The video explains that different colors of light have different wavelengths, with red light having the longest wavelength and violet the shortest. Wavelength is inversely proportional to frequency and directly proportional to energy, which is crucial for understanding the color spectrum and the behavior of light.

💡Frequency

Frequency refers to the number of wave cycles that pass a given point in a certain time period. In the context of the video, frequency is inversely proportional to wavelength and directly proportional to energy. The video uses the example of red and violet light to illustrate that violet light, with a higher frequency, has more energy than red light.

💡Apparent Depth

Apparent depth is an optical illusion where objects under water appear to be closer to the surface than they actually are. The video explains this phenomenon as a result of light bending, or refracting, when it moves from water to air. This concept is important for understanding how our perception of depth can be distorted by the refraction of light.

💡Rayleigh Scattering

Rayleigh scattering is the phenomenon where light is scattered in all directions by particles in the atmosphere. The video explains that this scattering is more effective for shorter wavelengths like blue and violet, which is why the sky appears blue. This concept is key to understanding the color of the sky and the reddish hues during sunrise and sunset.

💡Energy

Energy, in the context of light, refers to the amount of work that light can do. The video explains that the energy of a light wave is directly proportional to its frequency and inversely proportional to its wavelength. This relationship is important for understanding the behavior of different colors of light and their interactions with matter.

💡Prism

A prism is a transparent optical element with flat, polished surfaces that refract light. The video uses a prism to demonstrate the dispersion of light, where white light is split into its constituent colors. This concept is crucial for understanding how a prism can separate light into a spectrum, which is a fundamental principle in optics.

Highlights

Light is an electromagnetic wave and a transverse wave, exhibiting wave characteristics.

Sunlight is a mixture of visible colors, each with its own frequency and wavelength.

Refraction causes the separation of colors in sunlight, creating a rainbow effect when reflected on paper.

The human eye is sensitive to a narrow portion of the electromagnetic spectrum, which we perceive as light.

Apparent depth is an optical illusion caused by the bending of light when it passes from air into water.

Light does not require a medium to propagate and travels at different speeds in various media.

The speed of light is approximately 300 million meters per second in a vacuum.

Reflection allows us to see our image in a mirror and objects by the way light bounces off surfaces.

Diffused reflection occurs when light scatters in many directions off rough or uneven surfaces.

Specular reflection happens on smooth, flat, and shiny surfaces, allowing a clear image to form.

Dispersion is the separation of light into its colors due to differences in refraction, as seen in a prism.

A rainbow is formed by the dispersion of sunlight in water droplets, with light being refracted, reflected, and dispersed.

Red light has the highest wavelength and lowest frequency, while violet light has the lowest wavelength and highest frequency.

Wavelength and frequency are inversely proportional, while frequency and energy are directly proportional.

The sky appears blue due to Rayleigh scattering, which scatters shorter wavelengths like blue more effectively.

At sunset and sunrise, the sun appears red because longer wavelengths like red are less scattered by the atmosphere.

Light is the only type of electromagnetic wave visible to the human eye between infrared and ultraviolet waves.

Refraction is the bending of light when it travels from one medium to another of different optical densities.

Reflection of light is the bouncing back of light and depends on the surface of the object it strikes.

Transcripts

[Music]

can you imagine a world without light

or a world without the blue sky

how about a world without sunsets

even the smartphones we use every day

emit light

in this video we'll be talking about

light and how it gives color to our

world

we have learned previously that light is

an example of a transverse wave

thus it exhibits characteristics and

properties of a wave

specifically it is classified as an

electromagnetic wave

let's get started with this activity

fill a container with water clean the

surface

of a mirror and place it into container

at an angle below the surface level of

the water

place the container under the sun in a

position where the sunlight falls on the

surface of the mirror

hold a piece of white paper above the

container to catch the reflected rays

from the mirror

what did you see on the paper if you did

the activity right

you would see a rainbow reflected on a

paper

when the sunlight shone on the mirror

light first

enter the water and refract or bends

since sunlight is a mixture of visible

colors

each color has its own frequency and

wavelength

these colors refract at different angles

and get separated from each other

the separated colors are then reflected

from the mirror

to the paper

[Music]

the human eye is only sensitive to a

very narrow portion

of the electromagnetic spectrum lying

between the infrared

and ultraviolet we call this light

it is what was reflected on the paper in

the activity we just completed

you may have noticed that when someone

dives on a deep pool near you

it will look like the water is just

shallow if you are watching near and

above the surface of the water

this optical illusion is known as

apparent theft

apparent death is the illusion that

objects under the water appear to be

nearer to the surface than they really

are

this phenomenon is a consequence of the

bending of light

when light traverses the air water

boundary

unlike sound light does not need a

medium to propagate

it moves in its maximum speed in vacuum

but this speed decreases as it moves

along different media

this characteristic of light

consequently shows bending when it

crosses the boundary between

two media take this pencil in a glass of

water as an example

the two media for light is air and

liquid

apparent distortion of an object at the

boundary between media

is observed

refraction is the bending of light when

it travels from one medium to another of

different optical densities

the pencil in the water as shown is not

really broken

if we remove the water from the glass

and look at the pencil

the pencil's normal appearance is not

crooked

this distortion happens because of the

change in speed

and orientation of light with respect to

the normal as it traverses a new medium

of a different density

you may have noticed that when lightning

strikes from afar

a flash of light comes before you can

hear the thunder

this is because light travels faster

than sound

light travels at approximately 3 times

10

raised to the 8th power meters per

second or

300 million meters per second in a

vacuum

this speed decreases when light travels

in a dense medium

this means that the speed of light is

dependent on the properties of the

medium

[Music]

when you look at yourself in the mirror

you can see your reflection

but when you look at other objects you

can only see the object itself

these phenomena are caused by the way

light is reflected

if light is reflected on a rough

textured or

uneven surface such as paper it scatters

in many directions

this is called diffused reflection

diffused reflection

allows us to see objects from any angle

on the other hand regular or specular

reflection

happens when light strikes a smooth flat

and shiny surface such as a mirror

and is reflected in one direction it

enables us to see an image on the

surface

when a narrow beam of white light enters

a triangular block called a prism

the beam splits into a different range

of colors called spectrum

the process by which light is separated

into its colors

due to differences in degrees of

refraction is called dispersion

a rainbow is formed by the dispersion of

sunlight in drops of water

when sunlight passes through each

spherical raindrop

it is refracted and dispersed and then

internally reflected

one or more times before it finally

emerges out of the raindrop

the sunlight is again reflected and

wrapped at different angles

as passes through other drops

take a look at this illustration each

color corresponds to a given wavelength

and frequency

red light has the highest wavelength and

lowest frequency

while violet light has the lowest

wavelength and highest frequency

when we relate it to this table red

light

which has the highest wavelength and

lowest frequency

has the lowest energy while violet light

which has the lowest wavelength and

highest frequency

has the highest energy

thus we can say that the higher the

wavelength

the lower the energy which means that

wavelength and frequency

are inversely proportional on the other

hand

the higher the frequency the higher the

energy

frequency and energy are directly

proportional to each other

this is why red has the lowest energy

while violet has the highest energy

what makes the sunset and sunrise red

why is the sky blue the answers lie

in the composition of the atmosphere and

the nature of light waves

the atmosphere is a mixture of gases

droplets of water

and solid particles light travels in

straight lines as long as nothing

disturbs it

as light moves through the atmosphere it

bumps into bits of solid particles

or gas molecules and becomes scattered

in all directions

by either reflection or refraction

this phenomenon is known as rayleigh

scattering

named after the english physicist lord

john rayleigh

the angle through which sunlight is

scattered varies inversely as the fourth

power of the wavelength

hence blue and violet having shorter

wavelengths are scattered more

than orange and red the blue appearance

of the sky is a scattering phenomenon

as light moves through the atmosphere

most of the longer wavelengths pass

straight through

however much of the shorter wavelengths

like blue

interact with the gas molecules and

become scattered in the atmosphere

the atmosphere scatters violet light

more effectively

but our eyes are more sensitive to blue

since you see the blue light from

everywhere overhead

the sky looks blue now what makes the

sunset and sunrise red

at sunset are sunrise when the sun is

near the horizon

or low in the sky sunlight travels a

longer distance through the atmosphere

before it gets to your eyes

however the blue light is unable to pass

it becomes scattered in the atmosphere

before it even reaches your eyes

hence only the longer wavelengths such

as

orange and red are left making the sun

and the sky around it appear red or

orange

so to summarize light is an

electromagnetic wave and is the only

type of wave

visible to the human eye between the

infrared and ultraviolet wave

refraction of light is the bending of

light when it travels from one medium to

another of different optical densities

reflection of light is the bouncing back

of light and depends on the surface of

the object

wavelength and frequency are inversely

proportional

and frequency and energy are directly

proportional

that's all for now see you in our next

video

and don't forget to keep your minds busy

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