Light | Grade 8 Science DepEd MELC Quarter 1 Module 4 Part 3
Summary
TLDRThis 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
🌈 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.
🌞 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.
Mindmap
Keywords
💡Light
💡Electromagnetic Wave
💡Refraction
💡Reflection
💡Dispersion
💡Wavelength
💡Frequency
💡Apparent Depth
💡Rayleigh Scattering
💡Energy
💡Prism
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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