Full transcript
0:00there's a few properties of light that
0:02we can look at and firstly is the idea
0:04of reflection when light hits a surface
0:07it can reflect or bounce off of that
0:10surface and that's why in this image
0:12right here we get this nice beautiful
0:14dual image of the mountains you can see
0:18it's like a mirror image of the
0:19mountains reflected in the water light
0:21it's coming off the water towards us and
0:24we see the same image of the mountain
0:27again but some of that light will also
0:31actually pass through into the water
0:34some reflects off but some will go into
0:37the water and when it does it will
0:39refract or bend meaning light going into
0:43the water won't follow a straight line
0:45it would actually Bend when it passes
0:47into the water and that's true whether
0:50we're talking to water or if it was
0:52going from air to glass when it passes
0:55from one material to another light will
0:57actually refract or bend and one case of
1:02this is when we'd look at the light
1:04going to represent specifically white
1:07light when we look at the light coming
1:09from the Sun it's called white light and
1:12that's because it considered and
1:13consists of all the colors of the
1:16rainbow but when we see it we see white
1:19light I mean you shouldn't be staring at
1:21the Sun ever but if you see the light
1:22coming from it it looks white we don't
1:24see all different colors however if we
1:27take that light and we put it through a
1:30prism the dip we will actually see that
1:33it is made up of all the colors of a
1:35rainbow and what happens is when the
1:38light goes into the prism it refracts or
1:41bends you can see here's a nice example
1:43of it it doesn't follow a straight path
1:45it bends at the border between our
1:48medium here and the prism well
1:51the strange thing is the different
1:55colors will actually Bend different
1:58amounts because of their different
1:59wavelengths so red light and blue light
2:02or violet or yellow or green all Bend at
2:06slightly different angles
2:08and then when it comes out the other
2:11side of the prism it will Bend again and
2:13again all the different colors will pen
2:15slightly different and what happens is
2:17we get the white light dispersed
2:20dispersed into all the different colors
2:23so white light made up of all the colors
2:26we can use this prism to split it into
2:28all the different colors and see them
2:30and we see a nice beautiful rainbow of
2:33colors in fact this is why we see
2:36rainbows in the case of a rainbow the
2:39raindrops are acting as our prisms and
2:43now technically there's a little other
2:44complication and the fact that the light
2:46actually bends and like hits the back
2:49surface of the raindrop and then comes
2:51back but the idea is still the same the
2:53raindrop acts as a prism and takes the
2:56white light from the Sun and splits it
2:58into all the colors of the rainbow quite
3:01literally the rainbow in this case so we
3:04get this nice beautiful rainbow because
3:06the light is being split into all of its
3:09component covers because sunlight
3:11actually has it all in there but in
3:15science we can also use this because
3:18what will I use is a so-called
3:19spectrometer a spectrometer to study the
3:23spectrums of light so what we do is take
3:27white light and we can split it into the
3:29different colors and that to do that we
3:32use a spectrometer or and this whole
3:35process is called spectroscopy we're
3:37studying the spectrum of colors and
3:39really what you're doing is taking a
3:41light source say hey maybe this light
3:44from the Sun and we put it through this
3:46narrow slit the reason we're doing that
3:48is because we're narrowing it down to
3:49one beam of light put that through a
3:52prism and it splits it into our spectrum
3:55of colors and this is the simple setup
3:57of a spectrometer right here now what
4:01we're seeing right here when we see all
4:03of the colors in a rainbow is can tell
4:05called a continuous spectrum we're gonna
4:07see we get different type of spectra
4:09different types of these spectrums
4:11depending on what is our light source
4:13for a continuous spectrum what we have
4:16is some kind of hot dense gas or solid
4:20that would give a can
4:22tenuous spectrum of colors all the way
4:24from red through violet
4:26often we think of blue as the follower
4:29side but technically it's violet if we
4:31think of Roy G before remembering the
4:33colors but if we see all of the colors
4:36it's considered a continuous spectrum
4:38because you can see it's all the colors
4:40continuously with no breaks and that is
4:43once again when you have say a hot dense
4:48gas or a solid giving off the light but
4:53what can also happen is if we instead
4:56use for the light source a gas a
5:01low-density gas that we heat up what we
5:04find is we get a so-called emission
5:07spectrum emission spectrum or emission
5:10line spectrum and it looks like this or
5:13something like this anyway where we only
5:16get certain lines of color against a
5:19black background we are missing many of
5:21those lines we don't have all of the
5:23colors of rainbow we just get some lines
5:26against this background and now the
5:30thing is the spectrum we get depends on
5:34what the gas is made up of and we
5:37actually find each gas each atom of gas
5:40each element of gas whether we're using
5:42hydrogen or helium they would be very
5:45different they would each have their own
5:47unique pattern you can think of this
5:49like a barcode each element has its own
5:52unique pattern its own unique barcode so
5:56if you took gas that you had no idea
5:59what it was and if you were able to heat
6:01up this low-density gas run it through
6:03spectroscope or spectrometer we'd be
6:06able to determine what it is just by
6:08matching up the barcode against one that
6:10we know is we've mapped these all out in
6:12the lab and seen what they look like so
6:14we know all the different elements what
6:16their pattern should look like and again
6:19each one is unique that's kind of the
6:22neat thing about it so this is an
6:23emission spectrum where we don't have
6:26all of the continuous spectrum just
6:28certain lines within it and again each
6:33element has its own unique pattern and
6:35you can see
6:36this shows a little bit better they
6:38aren't gonna have all the colors in a
6:39rainbow different elements have their
6:41own unique little barcode if you will
6:44and you can compare that against a
6:45continuous spectrum where all the colors
6:47are there there whereas this is just
6:50certain lines so yeah already a very
6:54useful idea we can determine what the
6:57elements of a gas are