Full transcript
0:00we're gonna look at temperature for a
0:01second and now this is something you're
0:03probably familiar with I mean you maybe
0:05even look at what the temperature is
0:06before going outside so you know what to
0:08wear
0:09but the thing is temperature is actually
0:12a way of being able to measure how fast
0:15the particles within a material are
0:18moving so when we talk about the
0:19temperature of the Sun we actually can
0:22use that as a way of measuring how fast
0:25the particles in the Sun are moving and
0:28what we find is a hotter an object the
0:30faster the particles are moving okay
0:32okay well you might be asking why is
0:34this a born why do we think of
0:36temperature in this way or remember when
0:39those particles are moving around when
0:41they vibrate their electrons will give
0:44off electromagnetic radiation those
0:47charged particles giving off
0:49electromagnetic radiation so what we
0:52find is the hotter an object and again
0:55the faster particles it actually means
0:57that we get more intense higher energy
1:00radiation hotter objects will give more
1:04energetic electromagnetic radiation
1:06which also remember energy means friend
1:10is related to frequency so higher energy
1:12means higher frequency radiation so we
1:15can actually use the temperature to
1:17estimate how what the frequency of the
1:19radiation will be and we're also
1:23remember that higher frequency means
1:25shorter wavelength but the thing is even
1:32though a hotter object gives off higher
1:34frequency of radiation we also find that
1:36objects aren't just giving off one
1:38frequency or one wavelength no natural
1:42object is doing that and our Sun is no
1:44exception as you can see in this image
1:46here this is looking at the Sun at
1:49different wavelengths and you can see
1:50each of these images is quite different
1:53looking the Sun is giving off a range of
1:57different frequencies or different
1:59wavelengths depending on how you want to
2:00look at it
2:01and again we talked about this earlier
2:05the idea is we need to study all parts
2:07of the electromagnetic spectrum or
2:08missing part of the story cuz each of
2:10these images represents different areas
2:13different temperatures of the Sun
2:14different phenomenon occurring so if we
2:17did study them we would miss part of the
2:19picture and in this is just for our Sun
2:23that we're looking at but the same idea
2:25is for other objects they're gonna give
2:27off a range of different frequencies and
2:30we will find that there's a peak
2:32frequency or a peak wavelength if we
2:35want think in terms of wailings remember
2:37higher temperature actually would mean a
2:39shorter wavelength and this shows four
2:42different plots the closest one to our
2:44Sun would be the six thousand Kelvin one
2:46the surface is more about 5,800 which
2:49we'll talk about in a later chapter but
2:51this just demonstrates the idea that the
2:55frequency or wavelength does depend on
2:59the temperature of the object so as the
3:03temperature decreases we're getting to
3:05longer wavelengths but there's still a
3:07range of different frequencies given off
3:09you can see these objects are covering a
3:11wide range of frequencies and giving off
3:14different types of light or
3:16electromagnetic radiation across a range
3:18of the spectrum so we have to look at
3:20all of it to learn the picture but where
3:23the peak frequency is are you quite
3:24literally where the biggest most intense
3:26amount of light comes in that depends on
3:29the temperature and you can see it's
3:31shifting to the left for higher
3:32temperature curves so for the 6,000
3:36Kelvin we're getting to lower smaller
3:38wavelengths higher frequency higher
3:40energy and in this case the 6,001 Peaks
3:43in about the visible spectrum very
3:45similar to our Sun now one thing is
3:49we've been focusing a lot on suns and
3:51stars because hey it seems important for
3:54astronomy but it's important to know
3:57that like it's not just the star giving
4:01off radiation anything with moving
4:04charged particles will cause
4:06electromagnetic radiation which is
4:08pretty much everything including you
4:11problem is we aren't gonna show up on
4:14this curve I mean we're nowhere near
4:153,000 Kelvin no we are quite a bit
4:19cooler but we are still giving off
4:21radiation and in fact right now you're
4:23giving off infrared radiation now
4:27problem is obviously our eyes are not
4:28tuned to see that we see in the visible
4:30part of spectrum but if you have an
4:33infrared camera you can actually see the
4:35radiation given off by a person and at
4:39one of our science events there is a
4:42light and libation event they actually
4:44had an infrared camera and this image
4:46isn't the best quality because he was
4:48just taking on my phone but you can see
4:50this is an image of one of the physics
4:53graduates showing the infrared camera
4:56and you can see he was giving off light
5:00he was up the infrared variety but he
5:03was emitting light his glasses his
5:06sunglasses weren't his moustache also
5:08was a little colder you can see but he
5:11was radiating electromagnetic waves and
5:15this camera was entombed to see those
5:19rays so he was giving off radiation and
5:23again this idea that the peak frequency
5:26is related to the temperature this is
5:30also something you might have
5:31experienced in everyday life you just
5:33maybe didn't realize it even when you
5:35turn on your oven when you first start
5:38your oven especially if you have one of
5:39the old ones with the metal coils
5:41they're just dark but as they start to
5:44heat up what we find is the temperature
5:47is rising and we all start seeing a
5:50little bit of a mission in the visible
5:52part of the spectrum what do I mean well
5:55if you've turned them on they start to
5:57glow red
5:58after a while as they heat up they start
6:00to glow red that's because it's getting
6:01hot enough that part of the radiation
6:04that your coil on your oven is giving
6:07off is in the visible part it's not hot
6:10enough to give off the entire spectrum
6:12or glow white but it starts getting hot
6:15enough that you start seeing some infer
6:18a some of the visible light before that
6:20it would be giving off infrared but as
6:22it gets hot enough it starts to actually
6:25give off some visible light as well so
6:27as things heat up or if you're looking
6:30at a higher temperature object the peak
6:32frequency of the radiation goes more and
6:36more towards higher energy
6:38and this is incredibly useful for
6:41astronomy especially if we consider the
6:43maximum wavelength or maximum frequency
6:47if we think of this plot right here if
6:49we can figure out this peak frequency so
6:53we plot out the radiation coming from a
6:55star and see where the peak frequency is
6:57or peak wavelength we can determine the
7:00temperature of the object