- 4478 - LIGHT PHOTONS - how were they discovered? Einstein’s discovery of photons would be just one result in the growing awareness of the microscopic, quantum world. It was the first to claim that an entity in nature (in this case, the radiation of Maxwell discovered) was really made of quantum particles. That is photons.
--------------- 4478 - LIGHT PHOTONS - how were they discovered?
- Light comes to our eyes in little bundles of
energy, or are they very small particles?
Can we even discover the difference?
These questions all got started with a simple experiment that was all
the rage in the early 20th century. And as is usually the case, simple
experiments often go on to change the world, leading Einstein himself to open
the revolutionary door to the quantum world.
-
- Here’s the setup. You take a piece of metal.
You shine a light on it. You wait for the electrons in the metal to get enough
energy from the light that they pop off the surface and go flying out. You
point some electron-detector at the metal to measure the number and energy of
the electrons.
-
- The bizarre thing about this experiment,
measuring what’s known as the “photoelectric effect”, is that the electrons
didn’t behave as they should. If light is made of waves of electricity and
magnetism, as Maxwell taught us, then the electrons should be able to slowly
accumulate energy until they get hot enough to go flying off, regardless of the
frequency of light.
-
- And brighter more intense light should
lead to more energetic electrons, because there’s more energy available. But
neither of those expected outcomes happen.
Instead, only light above a certain frequency could get electrons to fly
off the surface. Those electrons always
left the metal with the same energy, no matter how intense the light was.
-
- Einstein thought about this problem for a
shockingly short amount of time before coming up with an elegant solution…that
once again reshaped our understanding of the physical universe. He supposed
that light itself was 'quantized”.
-
- What we perceive as undulating waves of
electricity and magnetism is really, at a deeper, more fundamental level, a
flood of discrete, distinct, indivisible little bundles of photons of light.
Each one of these bundles represents the smallest amount of light-stuff that
you can possibly have. And because these bundles are uncuttable, you cannot
have fractional proportions of light-stuff.
-
- You can have one unit of light-stuff, two
units of light-stuff, and so on, but never 2.56 units, or units. Somehow these
bundles, when enough of them come together, conspire to behave as if they were
waves of electricity and magnetism, but once you picked those waves apart you
would reveal their particle-like nature.
-
- This neatly solved the problem with the photoelectric
effect. Electrons need a certain amount of energy to get away from a metal. And
that energy isn’t determined by the brightness or intensity of the light, but
in its “frequency”.
-
- Higher frequencies correspond to more
energetic “photons”. If the energy was too low, the electrons could simply
never escape the metal. And when the photon strike the electrons, they deposit
a specific, fixed amount of energy, no more, no less, explaining why the
electrons always escaped in the exact same way.
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May 22, 2024 LIGHT PHOTONS - how were they discovered? 4478
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--------------------- --- Thursday, May 23, 2024
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