Hi. It’s Mr. Andersen and this is AP Physics
essentials video 123. It is on electromagnetic
radiation. Newton had shown that if you shine
white light into a prism it breaks it apart
into its different colors. And another scientist
wanted to know, is there any relationship
between different colors of light and the
temperatures. So William Herschel took a thermometer
and put it in the purple light and then the
blue light and the green and then the yellow
and in the red. And he wanted to figure out
where were the different temperatures dependent
upon color. But we wanted to have a control
in this experiment so we put another thermometer
right off on this side just to judge the room
temperature. And what he found surprisingly
is that that was the hottest temperature of
all. So what he really discovered was infrared
rays. And so those are rays that we can see
but generate a lot of heat. And so electromagnetic
radiation, we only see a small sliver of that
called visible light. But there is a whole
bunch of other electromagnetic radiation out
there in the universe. And we can put it on
a spectrum and measure it from the really
low small wavelength to the really long wavelengths
up to kilometers in wavelength. And then on
the other direction we are going to have increasing
frequency. So as we increase frequency we
are going to decrease that wavelength. As
we increase frequency in electromagnetic radiation
we are also increasing the amount of energy
that those waves have. And so if we start
with really high energy we would have gamma
rays then x-rays then infrared and then visible
lights. You can see that we are just seeing
a small sliver of electromagnetic radiation.
We then move into ultraviolet. Finally into
microwaves and radio waves. And so inside
this room right now I have visible light.
But there are also radio waves here. That
is how you can pick up a radio signal or a
tv signal. But I also probably have microwaves
in here as well. Hopefully I do not have too
many gamma rays in here right now. But if
we put them along a spectrum they are going
to decrease in wavelength as we move towards
those gamma rays. To give you a sense of scale,
radio waves are going to have wavelengths
around the size of a building but gamma rays
down around the size of a nuclei. And there
is this inverse relationship. So as we increase
wavelength we are going to decrease the amount
of frequency. And so as we increase frequency
we have higher amounts of energy. So which
one would you rather be exposed to? These
ones with long wavelength, really really low
frequency, low energy. The ones on the right
side are going to be able to damage cells,
ionize cells, cause damage to the cells itself.
And so did you learn to just make qualitative
comparisons based on wavelength and frequency
of electromagnetic radiation? I hope so. And
I hope that was helpful.
