The video explains the two primary types of reflection: specular and diffuse. Specular reflection occurs on smooth surfaces, obeying the law of reflection where the angle of incidence equals the angle of reflection, allowing for clear image formation. Diffuse reflection happens on rough surfaces, scattering light in multiple directions and preventing image formation.
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in this video we're going to try to
learn a little bit about reflection
or i guess you could say we are going to
reflect on reflection i think most of us
have a sense of what this is but we'll
try to get a little bit more exact about
it so there are actually two types of
reflection and everything that reflects
is doing one or the other or something
in between so we have two types let me
draw them so the first type and this is
kind of what we normally associate this
is what we normally associate with
reflection is specular reflection specular
specular reflection
reflection
and in specular reflection let's say
that this is the top of a of a mirror
this is a surface of a mirror if i have
a light ray coming in so let me draw a
light ray coming in and just to get the
terminology right this light ray coming
in this ray is the incident ray and it's
the incident ray because it's the ray as
it approaches the reflective surface let
me write that down
that right there is the incident ray in
in incident
incident incident
incident
ray it will approach the surface and you
can almost imagine that it bounces off
at essentially the same angle but in the
other direction so then it'll hit the
surface and then it'll bounce off and
it'll go just like that and then we
would call this the reflected ray after
it is kind of bounced off of the surface reflected
reflected
reflected ray and you may have already
noticed this if you've played around a
lot with mirrors you would see
and and we're going to look at some
images so you can think about it a
little better next time in front of the
bathroom mirror you can think about this
and think about the angle of incidence
and the angle of reflection but they're
actually equal so let me define them
right here so if i were to just drop a
straight line that is that is at a 90
degree or that's perpendicular to the
surface of the actual mirror right over here
here
we would define this
right here as the angle of incidence
i'll just use theta that's just a fancy
letter to show that the angle at which
we're coming in the angle between this
ray and the vertical right there that's
the angle of incidence and then the
angle between that vertical and the blue
ray right there
and the blue ray right there we call
that the angle of reflection and it's
just a property of especially mirrors
when you're having specular reflection
and you can see this for yourself at all
the esp well at all of the
you know regular mirrors that you might
experience is that
the angle of incidence is equal to
the angle
of reflection and actually we could see
that in a couple of images over here so
let me show you some images of specular
reflection just to make it clear here
so you have some light from the sun
hitting this mountain we're going to
talk about diffuse reflection a little
bit and that's what's happening it's
being reflected diffusely that's why we
don't see the actual image of the sun
here we just see the white but then that
those white light rays and they're
actually being scattered in every
direction some of them are hitting the
water so let's see this part i'm going
to try to match up parts of the mountain
so you have this part of the mountain
let me just in a better color you have
this part of the mountain up here and
the part of the reflection right over there
there
so what's happening right here is light
is coming from that part of the mountain
hitting this part of the surface of the water
water
hitting let me see if i can draw this
better it's hitting this part of the
surface of the water and then it's
getting reflected specular reflection to
our eyes and it's actually coming
straight at us but i'll draw at a slight
angle and then it's just coming straight
to our
and then it's coming straight to our
eyes like this if our eye was let's say
our eye was here it's actually coming
straight out at us so i actually should
just draw a vertical line
but hopefully this makes it clear and
what we just said the angle of incidence
is equal to the angle of reflection so
if you were to draw a vertical
if you were to draw a vertical and it
might not be that obvious here but this
angle right over here let me draw this a
little darker color this angle right
over here that's the angle
let me let me do that in a light color
this right here is the incident angle we
drew a vertical
and the angle at which the light ray is
approaching the surface of the water
right before it bounces that's the
incident angle relative to vertical and
then this angle right here i know it's
hard it doesn't look like they're the
same but that's just because of their
perspective that we're dealing with this
is the angle of reflection and they're
actually going to be equal and you can
also make a similar case and sometimes
my brain has easier thinking about this
if this angle is equal to that angle
this is what's defined to be the angle
of incidence and the angle of reflection
we also know that this angle right here
is going to be equal to that angle right
there and my brain sometimes thinks that
because that's kind of the angle between
the ray and the actual surface but
they're really the same notions
obviously it's a different angle but if
this is equal to that then this is equal
to that because these two are going to
add to 90 these two are going to add to
90. so another way you could view it is
so if we look at the surface of the
water the surface of the water is let me
draw a line along the surface of the water
water
another way to think about it if you can
is that this angle
this angle right over here is going to
be the same as this angle
right over there and you can also see it
in this reflection right over here so
the angle between the sun so this in the
light from the sun is going directly to
the water here
and then getting reflected at that point
on the surface of the water and then
coming over to our eyes and so we could
either say that this angle is equal to
this angle so the angle between the
incident ray and the surface of the
water is equal to the angle of the
reflected ray and the surface of the
water or
we could draw a perpendicular right over here
here
i'm not doing that too well
we can draw a perpendicular right over
here to the surface of the water and say
that the incident angle the angle of
incidence right there between the ray
and that perpendicular is going to be
the same as the reflected angle as it's
hard to see there once again because of
the perspective but hopefully that
starts to make sense and i encourage you
go to your bathroom and look in the
mirror and look at objects in the mirror
and think about the angle that the light
from the object must be hitting the
mirror for it to get to your eye and
where it's actually hitting the mirror
it's actually pretty it's a pretty
interesting thing to do if you're
looking for things to do in the in the bathroom
bathroom
now all we've talked about is specular
reflection but the other type of
reflection is diffuse reflection and
this is the type of reflection that it
may not be as obvious to you that it's
occurring everywhere you look diffuse
reflection
and in diffuse reflection because the
surface isn't smooth it's not a kind of
what we kind of associate as a mirrored surface
surface
so i'll draw it i'll zoom in a bunch so
in diffuse reflection maybe the surface
looks like that what happens is
is and let me be clear in specular
reflection any light ray that comes in
like that
the reflection will come off at the same
the angle of incidence will always be
equal to the angle of reflection this is
in a for the situation of say a mirror
it'll always be the same if i come in at
a steeper angle
if i come in at a steeper angle then
i'll go out at a steeper angle just like
that that's for specular reflection for
diffuse reflection all sorts of crazy
things happen and that's because we
don't have this really smooth surface or
the the molecules that make up the
surface do crazy things to light
so if i have if i come in in one
direction right over here over at that
point i might the light might reflect in
that direction although if i come in at
the same angle over here
now all of a sudden the light might go
in that direction and then if i come in
at the same angle
over here now a sudden the light might
go in that direction and if i come in i
think you get the general idea here if i
come in over here now the light might
scatter in that direction if i come in
if i come in over here
at the same angle now the light might
scatter in that direction so the general
idea is with diffuse reaction the the
reflected rays are going in all sorts of
crazy they're going in all sorts of
crazy directions and they're getting all
mixed up and so if you actually had an
image here so think about here if you
had an image here of the sun
and i'm not drawing it in particular but
let's say that these rays right here are
coming from an image are coming from
are coming directly from the sun then
when they reflect
it'll kind of preserve the image you'll
have the reflected image of the sun but
over here if all of these light rays are
coming from the sun they're not all
going off in the same direction this
will be a part of the sun part of the
sun it's happening at a really really
small level so you're really just
capturing the light but you're losing
all of the information from the actual
image and if you're wondering where
diffuse reflection occurs just look
around your room anything that's not a
mirror is reflecting diffusely it's
diffusing the light you see that here
the mountain right here is diffused for
reflection you have light coming from
the sun you have light coming from the
sun but that's being reflected in all
sorts of crazy directions in all sorts
of crazy directions so you don't see a
reflection of the sky over here the the
water here that specular reflection
because it's so so super smooth that it
preserves it the angle of incidence is
going to be the angle of reflection it's
always going to be the same angle
because it's a kind of almost perfectly
smooth surface the trees that's diffuse
reflection i also want to be clear on
something like the tree so on on
something that's white
and white is the entire spectrum of
light and we'll do more videos on that
in the future
it's reflecting the entire spectrum it's
just mixing it all up so you don't see
an actual reflection but if you look at
the trees if you look at the trees you have
have
the entire spectrum from the sun coming
down on the trees but the trees
themselves and you should watch the
videos on photosynthesis they're
observed they're absorbing every other
frequency of light except for the greens
you see
so they're just reflecting they're just
reflecting the green
they're just reflecting the green back
to us and they're doing it in a way
they're they're diffusely reflecting it
so we actually don't see an actual
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