Light As A Wave: Diffraction, Interference, Dispersion and Scattering

hello beloved students

in this lesson we are going to deal with

one of the lessons

in a subject in the senior high school

called physical science

come on join me

for today's lesson we are going to talk

about

light as a wave specifically on

dispersion scattering interference and

diffraction so our lesson objectives are

the following number one

define dispersion scattering

interference and diffraction

number two discuss the difference of

dispersion scattering interference and

diffraction number three

perform an experiment on the

interference and diffraction of light

and number four

cite applications of dispersion

scattering interference and diffraction

in real life experiences before we

proceed let us have first our quick

review

the previous module talks about

transmission reflection and refraction

of light

so when we say transmission what comes

to your mind so in physics

light can refer to any electromagnetic

wave

may it be gamma ray radio wave microwave

or the visible light when light travels

and strikes an object

a number of things can happen light may

be absorbed

reflected or transmitted when light

strikes a clear glass or tinted glass

light is said to be transmitted because

most of it

can pass through that said object with

this being said

there are three kinds of materials we

have transparent

translucent and opaque transparent

materials are those objects which allow

all light to pass through

such as clear glass our windows

or a glass of water meanwhile those

translucent materials are said

to allow some of the light to pass

through it

examples of such materials are our

tinted glass

the tinted windows of cars and our

sunglasses

lastly opaque materials are those

objects which does not allow light to be

transmitted

instead light is absorbed in these

objects

materials such as wood stone metals and

concrete are opaque to visible light

thus light cannot be transmitted but it

is

absorbed another thing that can happen

to light striking an

object is it being reflected reflection

of light happens when array of light

approaches a smooth

polished surface and the light ray

bounces back

the incoming ray is called the incident

ray

while the wave that is bounced away from

the surface

is called the reflected ray when a

straight line is drawn perpendicular to

the surface

that particular line is called the

normal line the angle formed

between the normal line and the incident

ray is called

the angle of incidence while the angle

formed

between the normal line and the

reflected ray is called the angle of

reflection

the law of reflection states that the

angle of incidence

is equal to the angle of reflection so

if the angle of incidence is 45 degrees

therefore the angle of reflection is

also 45 degrees

if the angle of reflection is 30 degrees

therefore the angle of incidence is also

30 degrees the amount of light reflected

by an object and how it is reflected

is highly dependent upon the degree of

smoothness or texture of the surface

when the surface is completely smooth

just like a plain mirror

it is said that virtually all of the

light is reflected equally

this type of reflection is called

specular reflection

however in the real world most objects

have convulated surfaces or rough

surfaces

this results to the incident light being

reflected in all directions

this particular reflection is called

diffuse reflection

we can see our own image as we look at

plane mirrors or even curved mirrors

which is an example

of specular reflection diffused

reflection on the other hand

does not allow us to see an image in

another instance

reflection can be annoying to people

just like when we are traveling or

driving at night

driving or traveling at night can be

difficult on a wet roadway

because of the annoying glare we get

from the headlights of the oncoming cars

the glare that we get is a result of the

specular reflection of the beam of light

from an oncoming car

normally a dry asphalt roadway diffuses

incident light this instance would make

traveling or driving at night

on a dry road easier compared

to driving on a wet road another thing

that can happen to light is

refraction refraction is the bending of

a wave when it passes from one

medium to another the bending is caused

due to the differences in the density

between the two substances

the tendency of array of light to bend

in one direction or another

is dependent upon whether the light wave

speeds up or slows down upon crossing

the boundary in the case of an

electromagnetic wave

the speed of the wave depends upon the

optical density of that material

the more optically dense a material is

the slower that a wave will move through

the material

one indicator of the optical density of

a material is the index of refraction

value

index of refraction values are numerical

index values

that are expressed relative to the speed

of light in a vacuum

now how do we know the amount of bending

first

let us define incident ray normal line

and the refracted ray the ray that

travels towards the boundary of two

medium is called the incident ray

while the ray that has passed through

the boundaries of two

media is called the refracted ray the

normal line drawn perpendicular

to the boundaries of two media is called

the normal ray the angle formed between

the normal

and the incident ray is called the angle

of incidence

meanwhile the angle formed between the

refracted ray and the normal line

is called the angle of refraction now if

a ray of light passes across the

boundary

of a material in which it travels fast

into a material

in which it travels slower then the

light ray will bend

towards the normal line however if array

of light

passes across the boundary from a

material in which it travels

slow into a material in which it travels

faster

then the light ray will be refracted

away

from the normal line one example of

refraction is when a pen or pencil is

placed in a glass

with water we can observe that the pen

or pencil is somehow cut

into two this is because

the refracted ray bends towards the

normal line

another example of refraction is when

you are looking at an aquarium

that is full of water the aquarium has a

glass

over the top and the sides if you stand

back a little

you can see the same fish through the

top of the tank

and the wall of the tank because you see

the light

coming through the glass at two

different points you see

two images of the same fish

the principle of refraction has many

applications in optics and technology

a lens uses refraction to form an image

of an

object for various purposes such as for

magnification

refraction is also used in peepholes of

house doors

cameras movie projectors and telescopes

since we have been reviewed let us now

proceed with our activity

you will be given with words which are

misspelled

you have to rearrange these letters to

form a sensible word

okay so number one what word is that

correct that's diffraction number two

that's right interference number three

scattering absolutely next number four

this person you got it all right good

job

in the next activity i will give the

definition of the word and you are going

to match the word to its correct

definition

so what word is defined as a phenomenon

in which

two waves superpose to form a resultant

wave of the lower

higher or same amplitude next

what word is defined as the slight

bending of light as it passes

around an object it is the spreading

white light into its full spectrum of

wavelengths

it is defined as a phenomenon in which

light rays get deviated from its

straight path on striking an obstacle

like dust gas molecules water vapor

and others

are you done let's reveal the correct

answers

did you get it right good job this time

we will do predict observe and explain

you will predict what will happen if i

do something

then observe then try to explain what

you have observed

so for this activity we are going to

make use of an interactive simulation

from

pet we will try to explore about

interference

and diffraction of light waves these two

objects at the left side are the light

sources with the color green

so if i press one of these light sources

what do you think will happen

if i press one of these i want you to

observe what happens

then i want you to describe what is

being formed

after i press this particular button

what they observe what shapes are formed

what colors are produced now i'll press

the second one

observe are there changes

[Music]

what colors are produced what patterns

have been observed why do you think does

this happen

[Music]

wave interference is a phenomenon that

occurs when two waves meet

while traveling along the same medium so

whenever the two light waves

interferes constructively with each

other

the two waves act to reinforce one

another and produce a super light wave

which are the color green ones on the

other hand

whenever light destructively interferes

they destroy each other and produce no

light wave or

the dark bands now let us proceed with

the diffraction of light

in the upper portion the one with the

red color

is the source of light in the middle is

a sheet where

a small hole is located on the other

sheath in the right most corner is the

sheath

where the light will be observed

what do you think will happen if i press

this

button to allow light to pass through

the sheet

with a small hole observe what happens

what pattern do you see what shape can

you see

what could be an explanation for this

pattern

this time let us try to change the

diameter of the hole

in the middle sheet do you think there

will be a change

in the pattern that we can observe

[Music]

with our manipulation of the diameter of

the hole

what do you notice to the patterns

observed

so diffraction is the slight bending of

light as it passes

around the edge of an object the amount

of bending depends on the relative size

of the wavelength of light to the size

of the opening

if the opening is much larger than the

light's wavelength

the bending will be almost unnoticeable

however

if the two are closer in size or equal

the amount of bending is considerable

and easily seen with a naked eye

let us now proceed with our lesson

proper

remember that the electromagnetic

spectrum could be

gamma rays x-rays ultraviolet rays

infrared visible light microwaves and

radio waves

the visible light spectrum is the

segment of the electromagnetic

spectrum that the human eye can view

more simply

this range of wavelengths is called

visible light

other portions of the spectrum have

wavelengths that are too large

or too small and energetic for the

biological limitations of our perception

typically our eye can detect

wavelengths from 380 to 700 nanometers

the visible light is composed of the

seven colors

red orange yellow green

blue indigo and violet violet has the

shortest wavelength at around

380 nanometers and red has the longest

wavelength at around 700 nanometers

visible light is a form of a transverse

wave

a transverse wave is a wave in which

particles of the medium move

in a direction perpendicular to the

direction that the wave moves

transverse waves are always

characterized by particle motion

being perpendicular to the wave's motion

a transverse wave has the following

characteristics

wavelength crest amplitude

trough and origin the line drawn

through the center of the diagram

represents

the origin the equilibrium or the rest

position

of the wing the crest of a wave

is the point on the medium that exhibits

the maximum amount of positive or upward

displacement

from the rest position the trough on the

other hand

exhibits the maximum amount of negative

or

downward displacement from the rest

position

the amplitude of a wave refers to the

maximum amount of displacement of a

particle on the medium

from its rest position lastly the

wavelength of a wave is simply the

length of one complete wave cycle

so a wavelength can be measured as a

distance from crest to crest

or from trough to trough long ago in the

science community it was believed

that light was composed of a stream of

particles

however it was a british erudite and

physician called thomas young

who convincingly demonstrated the wave

nature of light

through his double slit experiment known

today as the young's life interference

experiment when the waves emerging from

two narrow slits are superimposed on a

screen

placed at some distance parallel to the

line connecting these lids

a pattern of bright and dark fringes

regularly spaced

appears on the screen this is what he

calls as

the interference pattern this is the

first

clear proof that light added to light

can produce

darkness this is what we have observed

also

in our interactive simulation that we

have done

a while ago in order to observe

interference in lightweights the

following conditions must be met

first the sources must be coherent that

is

they must maintain a constant phase with

respect to each other

second the sources should be

monochromatic

that is of a single wavelength

now there are two types of interference

we have constructive

and destructive interference

constructive interference takes place

when the crest of one waves

falls on the crest of another wave such

that the amplitude is maximum

these waves will have the same

displacement and are in the same phase

in the opposite manner destructive

interference happens

when the crest of one wave falls on the

trough

of another wave such that the amplitude

is minimum

the displacement and phase of these

waves are not the same

then let's proceed with diffraction

diffraction is the slight bending of

light as it passes around the edge of an

object

the amount of bending depends on the

relative size of the wavelength of life

to the size of the opening if the

opening is much larger than the light's

wavelength

the bending will be most unnoticeable

however if the two

are closer in size or equal the amount

of bending is considerable and easily

seen with the naked eye

in the visible light spectrum red with

the longest wavelength

is diffracted the most and violet with

the shortest wavelength

is diffracted the least because each

color is diffracted a different amount

each color bends at a different angle

the result now is dispersion

dispersion of light occurs when white

light is separated into its different

constituent

colors red orange yellow

green blue indigo and violet

because of refraction visible light or

white light can be split up to form a

spectrum

using a prism a prism is a block of

glass

with a triangular cross section as

visible light waves

enter the glass they are refracted

because they are slowed down

from the air as it enters the glass

the spectrum of colors is produced

because

different colors of light travel at

different speeds in glass

red light is slowed down the list by

glass and is refracted

the least violet light is slowed down

the most by glass

and is refracted the most as a result

the colored light spreads out to form a

spectrum of white light

so what then is scattering of light

when sunlight enters the atmosphere of

the earth the atoms and molecules of

different

gases dust particles water vapor

in the air absorb the light then these

atoms

re-emit light in all directions

this process is known as the scattering

of light

the intensity of the scattered light

depends on the wavelength of the light

and the size of the particles air

molecules and other particles

that scatter light are called scatterers

scatterers don't scatter all the colors

equally

instead they scatter the shorter

wavelengths

violet blue and green in greater amounts

than the longer wavelengths yellow

orange and red

this type of scattering is called

selective scattering or

also known as the rayleigh scattering

this explains

why we have a blue sky during the day

and

a reddish sky during sunset

another type of scattering is the maze

scattering or the may effect

cloud droplets with a diameter of 20

micrometers or so

are large enough to scatter all visible

wavelengths

more or less equally this means that

almost all of the light which enters the

clouds

will be scattered because all

wavelengths are scattered

clouds appear to be white when clouds

become very deep and heavy

less and less of the incoming solar

radiation makes it through to the bottom

of the cloud

which gives this cloud a darker

appearance

now that you have learned about these

four terms

how are you going to differentiate them

from each other

now i want you to try to differentiate

and describe these terms using your own

words

using your own language so i would know

that you really have understood this

lesson

after our discussion with interference

diffraction dispersion and scattering

let us now go over the different

applications

of these terms first off is diffraction

do you notice the different colors in a

cd or dvd

we also have the shadow these two

pictures

could be explained by the diffraction of

light

next is we have interference what do you

see

in the first picture we can see that the

soil has a liquid with different colors

have you seen or experienced such

event if you have spilled to the land

a certain oil or kerosene or gasoline

then probably you have seen such events

[Music]

in the second picture we can observe

that there is a bubble

a bubble of soap with different colors

around it again these two pictures can

be explained by

interference of light then we have

dispersion of light

in the first picture we can see a

rainbow is formed in the sky

and in the second picture white light

enters a prism and it separates into

different colors

lastly we have scattering of light

mentioned earlier we have the blue color

of the sky

the white clouds and we have the reddish

sky

during sunset let us now check your

understanding of our topic today

this is known as pick a number so once

you pick a number

a question will be shown and you have to

answer it

let's begin pick a number from one

two three four and five have number two

[Music]

it is responsible for the alternating

light and dark bands

when light passes through two or more

narrow slits

what is it

then choose again another number so

number one

it is responsible for light spreading as

it passes through

a narrow slit

what is it

next number okay you chose number three

it occurs when molecules are more

capable of scattering

a selected wavelength of light what term

is being described

then choose again another number

k number five the reddish sky during

sunset

as well as the blue sky can be explained

by

blanc finally we have number four

is responsible for the bending of white

light into different spectrum of colors

what is it have you answered it all

correctly

congratulations for your assignment

i want you to do performance task number

three

first you have to take a selfie picture

with one of the applications of any

light phenomena

second write the correct explanation

as to why such phenomenon occurs

remember that during the discussion in

this video lesson

i have just presented the different

light phenomena

but i have not explained as to the

detail

why such phenomenon occurs so that will

be

your task for the performance task

number three

once you are done you have to print your

output in a bun paper

for those students whose modality

belongs to

the modular printed while for those who

are

under the modular digital you may just

send a soft copy of your output

through my email or through my messenger

submission of your performance task will

be on or before

june 18 2021 that is one week from now

here is how you will be scored with your

performance task

first correctness of explanation that is

worth 20 points quality of your selfie

picture that is 15 points

creativity of your presentation that is

10 points

and timeliness of submission will get

you

5 points a total of 50 points for this

performance task

as we come to an end in this lesson i

will leave you with this particular

quote

by douglas pales sometimes it is

important to work for that pot of gold

but other times it is essential to take

time off

and to make sure that your most

important decision in the day

simply consists of choosing which color

to slide down

on a rainbow thank you so much for

watching

i hope you learned something today

please don't forget to like

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students will also be informed

stay tuned for more videos goodbye