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Chemistry: 4.8 Photons 45 Views
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Description:
When you turn on a light, what comes out? Friends...or photons? Well, you'll know the answer as soon as you watch this video.
Transcript
- 00:04
Many great scientific minds have combined their efforts to help us arrive
- 00:08
at our current understanding of what we [Hertz, Einstein and Lenard paintings]
- 00:10
today call the "photoelectric effect,"
- 00:13
which is what happens when light strikes
- 00:15
a metal and the resulting energy
Full Transcript
- 00:18
transfer causes electrons to be emitted.
- 00:21
Of course, not all of these scientific [Hertz stood in a lab]
- 00:23
greats performed their experiments in the
- 00:24
same place and at the same time but it's
- 00:26
a whole lot more fun to pretend that they did, so
- 00:29
here we go. First, we've got the German
- 00:31
physicist Heinrich Hertz, who discovered [Hertz waving in a lab]
- 00:34
while working with a spark-gap
- 00:36
transmitter, which is an über-old radio
- 00:39
broadcasting device, that substances
- 00:41
would sometimes give off a spark after
- 00:43
absorbing light. Rather than chalking the
- 00:46
phenomenon up to it being late and the
- 00:48
fact that he hadn't slept much in the
- 00:49
past week, Hertz continued to study the [Hertz using a flash light on the spark-gap transmitter]
- 00:52
effect, which has been sometimes
- 00:53
referred to as the "Hertz effect." So yeah,
- 00:57
nothing to do with rental cars. The next [Hertz appears at a car rental store]
- 00:59
guy to throw his hat into the lab was
- 01:01
Phillipp Lenard, who was a former
- 01:04
assistant of Hertz's. So it makes sense that [Lenard walks into the lab]
- 01:07
they'd both be there, right? Well, Lenard
- 01:09
piggybacked on Hertz's research and
- 01:11
eventually put together a little [Lenard giving Hertz a piggyback]
- 01:12
experiment of his own that shed a lot of...
- 01:14
light... on the subject. He wanted to test
- 01:17
the theory of thermal emission posed by
- 01:20
classical mechanics that when light
- 01:23
shines on a surface, the transfer of
- 01:25
energy to that surface increases the
- 01:28
energy of the particles, which in turn
- 01:30
emit electrons. So, he built this thing:
- 01:33
cathode here, anode here, and this thing [Finger points to cathode and anode]
- 01:36
is a vacuum tube, and an ammeter here to
- 01:39
measure the current. Well, when Lenard let
- 01:42
lights of varying intensity reach the [Lenard using a flash light on the transmitter]
- 01:44
cathode, he found that below a certain
- 01:46
threshold frequency, no electrons at all
- 01:49
were emitted, while above that threshold
- 01:51
frequency, the number of electrons that
- 01:54
made their way to the anode was
- 01:55
proportional to the intensity of the
- 01:58
light. So what Lenard observed flew a bit
- 02:00
in the face of classical physics. There [Electrons flying around Lenard]
- 02:02
had to be some mysterious explanation
- 02:05
for what was happening. Enter Albert
- 02:07
Einstein. Go ahead, squeeze on in
- 02:09
there Albert; they'll make space for you. [Einstein squeezes in between Hertz and Lenard]
- 02:11
Albert introduced the idea of "photons,"
- 02:14
basically packets of light that aren't
- 02:16
just waves, but also actual particles of
- 02:19
energy. Einstein's theory of
- 02:21
wave-particle duality proposed that [Electrons moving around]
- 02:23
these photons would strike electrons and
- 02:25
force them to say au revoir to
- 02:27
their atom. Kind of like a new boyfriend
- 02:29
moving in in the old one moving out. You [Boyfriend moves out of house and Lenard appears]
- 02:31
know what we're talking about, there,
- 02:32
Lenard. Anyway, Einstein found that
- 02:35
each electron will only be ejected from
- 02:38
its atom if the frequency of light is [Rainbow colored light with different frequencies]
- 02:41
high enough. Well, this discovery
- 02:43
kickstarted something we now call
- 02:44
"quantum mechanics." Yeah, just those words
- 02:48
are enough to give you a headache, but it
- 02:49
was a huge breakthrough in the
- 02:50
understanding of light, energy, and
- 02:52
thermodynamics, and... Okay, that was bound [Hertz and Lenard shaking hands and Einstein giving thumbs up]
- 02:55
to happen.
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