Full transcript
0:01but the problem is life is even more
0:05confusing than we might think we've been
0:08talking about it as a wave but what
0:11we've actually seen in experiments is
0:14that light is just bizarre it doesn't
0:16only behave as a wave light can also
0:21behave as a particle it can behave as a
0:25wave or a particle and often one the
0:27best ways to think of it is when you're
0:29looking at a larger scale it's easier to
0:31think of it as a wave when you're
0:32looking at a really small scale we think
0:34of it as a particle it's not a perfect
0:36definition I'm giving you here but it's
0:40helpful and you will see that this idea
0:42of wave and light as a particle will be
0:44very important for us and what we need
0:47to do is define these particles these
0:49light particles these electromagnetic
0:50particles are photons so light can be
0:55described as a wave or as a photon which
0:58is a particle and what we find is that
1:01when we talk about the frequency of the
1:05wave that relates to the energy of the
1:08photon that's how we combine these two
1:10ideas how we relate them so what we see
1:13is these two things are proportional so
1:15if a wave is high-frequency
1:17it also means we can describe it as high
1:19energy a high-energy photon so take time
1:24to absorb that idea the energy we talk
1:27about high energy also means high
1:29frequency but remember that would mean
1:32that we'd be looking at small wavelength
1:35from the previous slide large frequency
1:39small wavelength large frequency large
1:42energy so a bunch of ideas that relate
1:45together but we also have to look at
1:49light in general light in general and
1:51look at one of the things that you
1:54probably know intuitively you might not
1:57realize if you know it intuitively and
1:59that light gets less bright the further
2:02you are from the source and when you
2:04think about it this makes some sense if
2:06I mean as you walk away from a
2:08streetlight it seems to dim when you
2:10look back it doesn't seem as bright
2:13and like you've seen probably many many
2:14examples of this in your everyday life
2:17when you walk away from a light source
2:19it gets dimmer or seems to get dimmer of
2:22course if you walk back up to the light
2:23source you'll realize it hasn't dimmed
2:25it was just from your perspective it
2:27seemed to get dimmer why is that well
2:30this image shows it very nicely light
2:33from an object goes in all directions so
2:36light coming from our Sun doesn't just
2:38come to us it goes in all directions
2:41towards a sphere it makes a sphere of
2:43light spreading out from the Sun but you
2:47can think that the light from the Sun
2:50that was spit out well there was a set
2:52amount of it and then as it starts to
2:55travel further and further away from the
2:57Sun that amount of light has to be
3:00spread out over a wider and wider area
3:03so that's why it seems to get dimmer the
3:06further you are from the source because
3:08the intensity of the light the amount of
3:11light the energy is being spread out
3:12over a larger area the larger surface of
3:15a sphere the sphere gets larger and
3:18larger further you get from that object
3:19and thus the amount of energy per area
3:23gets smaller so it looks at the dimmer
3:25and it actually gets dimmer at the
3:27square of the distance and that's just
3:29because the surface area of a sphere is
3:31related to the square of the distance so
3:33the further you are the energy would get
3:36dimmer so if we double the distance it
3:41actually becomes four times less bright
3:44because it's the square of the distance
3:46so three times the distance nine times
3:49less bright four times 16 times I sprite
3:52take the number squared that's how less
3:55bright it will get the further you go