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Many great scientific minds have combined their efforts to help us arrive

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at our current understanding of what we [Hertz, Einstein and Lenard paintings]

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today call the "photoelectric effect,"

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which is what happens when light strikes

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a metal and the resulting energy

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transfer causes electrons to be emitted.

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Of course, not all of these scientific [Hertz stood in a lab]

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greats performed their experiments in the

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same place and at the same time but it's

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a whole lot more fun to pretend that they did, so

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here we go. First, we've got the German

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physicist Heinrich Hertz, who discovered [Hertz waving in a lab]

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while working with a spark-gap

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transmitter, which is an über-old radio

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broadcasting device, that substances

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would sometimes give off a spark after

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absorbing light. Rather than chalking the

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phenomenon up to it being late and the

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fact that he hadn't slept much in the

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past week, Hertz continued to study the [Hertz using a flash light on the spark-gap transmitter]

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effect, which has been sometimes

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referred to as the "Hertz effect." So yeah,

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nothing to do with rental cars. The next [Hertz appears at a car rental store]

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guy to throw his hat into the lab was

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Phillipp Lenard, who was a former

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assistant of Hertz's. So it makes sense that [Lenard walks into the lab]

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they'd both be there, right? Well, Lenard

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piggybacked on Hertz's research and

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eventually put together a little [Lenard giving Hertz a piggyback]

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experiment of his own that shed a lot of...

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light... on the subject. He wanted to test

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the theory of thermal emission posed by

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classical mechanics that when light

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shines on a surface, the transfer of

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energy to that surface increases the

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energy of the particles, which in turn

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emit electrons. So, he built this thing:

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cathode here, anode here, and this thing [Finger points to cathode and anode]

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is a vacuum tube, and an ammeter here to

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measure the current. Well, when Lenard let

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lights of varying intensity reach the [Lenard using a flash light on the transmitter]

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cathode, he found that below a certain

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threshold frequency, no electrons at all

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were emitted, while above that threshold

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frequency, the number of electrons that

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made their way to the anode was

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proportional to the intensity of the

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light. So what Lenard observed flew a bit

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in the face of classical physics. There [Electrons flying around Lenard]

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had to be some mysterious explanation

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for what was happening. Enter Albert

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Einstein. Go ahead, squeeze on in

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there Albert; they'll make space for you. [Einstein squeezes in between Hertz and Lenard]

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Albert introduced the idea of "photons,"

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basically packets of light that aren't

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just waves, but also actual particles of

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energy. Einstein's theory of

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wave-particle duality proposed that [Electrons moving around]

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these photons would strike electrons and

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force them to say au revoir to

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their atom. Kind of like a new boyfriend

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moving in in the old one moving out. You [Boyfriend moves out of house and Lenard appears]

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know what we're talking about, there,

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Lenard. Anyway, Einstein found that

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each electron will only be ejected from

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its atom if the frequency of light is [Rainbow colored light with different frequencies]

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high enough. Well, this discovery

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kickstarted something we now call

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"quantum mechanics." Yeah, just those words

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are enough to give you a headache, but it

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was a huge breakthrough in the

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understanding of light, energy, and

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thermodynamics, and... Okay, that was bound [Hertz and Lenard shaking hands and Einstein giving thumbs up]

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to happen.

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