Wave-Particle Duality and Photoelectric Effect - Atomic Structure Video

hey it's professor Dave, I want to tell you
about wave-particle duality
so let's take a break from atoms look at something else
light. for some time we had known light
to behave as an
electromagnetic wave, for this reason
light is also called electromagnetic
radiation
light waves have both a wavelength, the
distance from tip to tip
and a frequency, the number of waves that
pass by a point per unit time
they are inversely proportional since the
shorter the wave
the more of them that can go by per
second resulting in a higher frequency
these variables are related by the
following equation:
in which c is the speed of light, about
300 million meters per second
the speed limit of the universe. the
electromagnetic spectrum
shows light of all the different
wavelengths from gamma rays to radio
waves
including this tiny sliver in the middle
which is visible light
the light we can detect with our eyeballs.
the wave theory of light
was very useful for a time but it could
not explain
the photoelectric effect. this was the
observation
that if a certain metal plate is
irradiated with light an electron is
ejected
which can be detected when it interacts
with a positively charged wire or
plate sensor.
the incongruity was that the ability of
the light to eject an electron
depends only on its frequency and not
its intensity
so if the beam was below a certain
frequency even a very intense beam
with a lot of light could not eject an
electron whereas
above a certain frequency the faintest
beam possible
could do it. this seem strange and a
famous fellow named
albert Einstein solved the problem by
extending a concept developed by max
planck
just five years prior. planck proposed that
energy is not continuous
but rather is quantized, that is all
energies
are multiples of the smallest fundamental
unit of energy
the plank energy. in fact quantum theory
went on to show that everything is
quantized
space and time too, so you can't
infinitely subdivide them
you'll eventually get to a smallest
thing that can't be divided further
but more on that in the physics course.
einstein extended what planck said
about energy
and rationalized that light must also be
made of quanta
which he called photons. these are
particles of light
this explains the photoelectric effect
because an electron is ejected
when struck by a singular photon with
sufficient energy
it only takes one photon so even the
faintest beam
above a certain frequency will be able
to do it but if none of them are of that
minimum energy
no matter how many photons strike the
sample an electron will not be ejected
it was found that the energy of the
photon can be given by the following
equation:
according to the frequency of the photon
and planck's constant
we now have to accept that light obeys
wave-particle duality, meaning it is both a
particle
and a wave at the same time. confused? you should be
this is the first discovery in a series
that brought about the quantum
revolution
completely changing the landscape of
physics and how we view the universe
Newton's Laws no longer reign supreme
in the world of the very small and the
universe became much stranger
almost overnight thanks to Einstein and
others
that were inspired by him. thanks for
watching guys, subscribe to my channel
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and as always feel free to email me