Hi. It's Paul Andersen and this
is disciplinary core idea PS4B which is on
electromagnetic radiation. Electromagnetic
radiation is light. Light you might see in
a rainbow. Or better yet, a double rainbow.
But it's also radio waves and x-rays and gamma
rays. It's incredibly important because there
are really only two ways we can move energy
from place to place. One of those ways is
using what's called a particle. So an object
moving from place to place. And another way
is moving a wave. But what's interesting about
electromagnetic radiation is it's both a particle
and a wave. Especially as we start digging
into quantum theory. And so specifically though,
what is light? Light is electromagnetic radiation
with a specific frequency. And so when you're
looking at green light, green has a specific
frequency. And we perceive it as green. Likewise
red would have a different frequency. And
there's a lot of frequencies of electromagnetic
radiation that we can't see. And so if we
change the frequency we might have radio waves.
You can't see those. But they're all around
us. Likewise x-rays as well. X-rays that you
might get if you break a bone. We can't see
them, but it doesn't mean that they're not
there. And so all of these are part of what's
called the electromagnetic spectrum. And it
varies all the way from radio waves with really
really long wavelengths, about the size of
a building. To waves that have a really really
small wavelength the size of an atom. And
they also have varying frequencies. Relatively
low frequency. That's the number of waves
per second to incredibly high frequency. And
as we move up on this side of the electromagnetic
spectrum they're carrying more energy. And
as a result they can be dangerous. But also
useful. And so if you look at an x-ray for
example. It can not just bounce off our body
like visible light does. It can move through
our body. And so it doesn't move through all
the parts of our body equally. It's going
to bounce back when we have dense objects,
like your bones. But it's going to move through
soft tissues. And so we can look at how many
of those X-rays are making through and we
can really get an image on what's on the inside
of our body. But all of these things up on
this end of the spectrum are dangerous. And
high amounts of those can damage our cells.
Now there's some properties of electromagnetic
radiation, like all waves, that as light hits
and changes from one medium to another it
can actually refract or it can bend. Now some
of it might reflect and some of it might transmit
through. But it can definitely bend as it's
moving from mediums. And the reason why is
that it's actually traveling at different
speeds. There's some other phenomena that
you should understand about electromagnetic
radiation. As we increase the heat of an object,
so as we increase the heat it's going to give
off different electromagnetic radiation. And
so we can look out at space and we can see
based on the electromagnetic radiation that
we're getting, we can tell the heat of objects,
like stars, found in space. Also matter is
going to give off different light based on
what it is. And so these are called emission
spectrum. And so a great place you could see
this would be in a chemistry classroom where
you're burning objects or heating them up
and you're looking at the light that comes
off of that. Now we'll just see it as one
color of light. And so we have to use a prism
or a diffraction grading to spread it apart
so we can see what colors of light are found
in there. But it's almost like a fingerprint
of what the atom is. And so we can look at
light. We can break it apart into its different
wave lengths and we can figure out of this
is hydrogen. Or this is iron. And so that
again tells us more information. And then
if we were to look in a nuclei, and nuclei
as it's starting to decay is going to give
off gamma radiation so we can really tell
what's going on inside the atom itself. And
so how do you teach this? Well in the lower
elementary grades you want to talk about light.
And the idea that everything is dark if we
don't have light. And everything you see is
the reflection of light. And so once we add
light we start to pick up objects. And the
students should understand what you're really
seeing is the light bounce off those objects
back to you. And we can block that light.
So we could put something transparent and
the light is going to move through it, but
we could vary the transparency and we could
make it real opaque. And the light can't get
through. And if light can't get through, it's
going to produce a shadow on the other side.
Also in the lower elementary grades you want
to introduce the idea of mirrors and prisms.
And what they can do is they can redirect
light. They can move light in a different
direction. So a mirror is going to bounce
light off of it. And a prism is going to change
the angle at which the light is moving. And
kids love to play around with prisms. As you
move into the upper elementary grades you
want them to understand that what we see in
the universe gets to us through light. And
it gets to us through nothingness. It get's
to use through the nothingness of space. And
so that light is traveling sometimes millions
and millions of years before it actually reaches
us. But what's interesting is that we can
bend that light using lenses and we can build
telescopes that can magnify the amount of
light that we're getting. And so we can see
the universe a little bit better. As we move
into middle school we want students to understand
that light can be reflected, absorbed and
transmitted. And we see as a result of all
of these things. And so the light that is
hitting this painting, some of it is being
absorbed. Some of if it is being transmitted
through. And some of it is being reflected.
And the frequency and the wavelength of the
light that's coming back to us is going to
give us its color. And so we're getting blue
from this part of the painting because it's
absorbing the other colors. And what about
white? White is the reflection of all of that
visible light. And black is the reflection
of none of that visible light. And so that's
important that they understand that. And also
they should understand that light will always
travel in a straight line. It will always
travel at a specific speed, the speed of light.
And it will travel in a straight line until
it moves from medium to medium. In other words
as it travels from air into water or air into
glass, it can be refracted or it can be bent.
And as a result of that you can see the prism
right here is bending the light. Each of these
wavelengths of light are going to bend a little
bit more. And so we can break it apart into
its different colors. Likewise if we remove
the medium, what's interesting about electromagnetic
radiation, like light, is that it can move
right through it. And so it can move through
it just like a wave might. But sound can't
travel in space. And electromagnetic radiation
can. As we move into high school we want students
to understand that particles and wave move
material and move energy from one place to
another. And quantum theory explains how electromagnetic
radiation is both a particle and a wave at
the same point. But you don't need to dig
too deep into quantum theory. Another property
of light that's interesting is if you have
very small objects we really can't see them.
And that's because they're smaller than the
wavelength itself. If we increase the wavelength,
and we incident with matter, what can happen
to that light? Well lot's of times it can
be absorbed and be converted into something
like heat. Sometimes it can move through material.
Sometimes it can ionize material and damage
cells. That's how an x-ray works. And sometimes
as it bounces off it's going to give us an
emission spectrum. In other words we're going
to see what colors of light are reflected
and transmitted through that medium and we
can tell what that medium is. And then also
remember atoms can give us information about
what's going on inside the nucleus based on
the waves that they're giving off. Gamma rays
as well. And so I hope that was helpful.}
