Hi. It’s Mr. Andersen and this is AP Physics essentials video 124. It is on electromagnetic
waves, which are the oscillations that create electromagnetic radiation. And they are important.
And so light is electromagnetic radiation and therefore it is carried in these electromagnetic
waves. And does light make it from the sun to the earth? Of course. And so that means
that electromagnetic waves can make it through the vacuum of space. But can you hear the
sun? No. And that means that the mechanical sound waves are not able to transfer through
space. If they could scientists have estimated that the sound of the sun would be around
100 decibels. So that is about the sound of a jackhammer a few meters away. So it would
be deafening in sound. So it is a good thing that we do not hear the sun. But it is really
important that we see it. That those electromagnetic waves make it here. It keeps us warm. It also
allows plants to grow and so we can survive. And so the electromagnetic spectrum is made
up of these electromagnetic waves. And they go from high energy, really high frequency
low wave length gamma rays all the way down to long wavelength low energy radio waves.
Remember you are only seeing a small portion of that. But the one thing these all have
in common is that they are made up of electromagnetic waves. Those are transverse waves. Remember
what a transverse wave is, is one where the oscillations are perpendicular or at ninety
degrees to the direction of the movement of the wave. And so it is not only in one dimension,
we also have electric fields and magnetic fields that are perpendicular to themselves.
And so we have oscillations that are both perpendicular to the direction of motion and
the corresponding field. And so they can travel through anything. Electromagnetic waves can
travel through medium like light can move through water obviously. Or radio waves can
move through the walls of my house so I can hear the radio. But they can also move through
the vacuum of space. And so if we look at electromagnetic waves, remember as we move
towards high energy gamma rays our wavelength is decreasing but our frequency is increasing.
So radio waves have really long wavelengths around the size of a building where as gamma
rays would be more the size of an atom itself. But if we look at how they oscillate, remember
the wave is going to move in this direction and the oscillation is going to be perpendicular
to that. But adding on top of that we also have these fields. And so the direction of
the wave is going to be, we will say, from left to right in this dimension. But we are
also going to have, in the Z dimension, we are going to have these electric fields that
oscillate back and forth. And then in the Y or rather in the X we are going to have
magnetic fields that go back and forth. And so to give you a visual of what they really
look like, we have these oscillations in these two dimensions and then the movement is going
to be in the third dimension. And that starts to explain why we have things like the right-hand
rule when it comes to electricity. And so energy can move from point A to point B in
two ways. It could move as a particle. We could shot a particle from A to B. But the
other way we can transfer energy is through a wave. We could oscillate, for example the
water here, we could oscillate it back and forth. That would create waves that could
move B back and forth. Now that would be a mechanical wave because we physically have
to have a medium to transfer the energy from one to another. But electromagnetic waves
are not mechanical. That means they could move through the water, they could move through
the medium but they could also move through the vacuum of space. And so did you learn
to describe the model of an electromagnetic wave? It is both a transverse perpendicular
to electric field and magnetic field. And also it can move through the vacuum of space.
And I hope that was helpful.