Particle Nature of Light-Photon Video Lecture - NEET

you
this video is all about photons and what
they actually are and also a bit of a
start to looking at quantum physics
which is a bit that you don't really do
GTS cm sounds pretty a pretty cool
exciting however it's not as bad as it's
sometimes made out to be so a lot of
work had gone on for a long time looking
at both the wave model and the particle
model for light a Newton thought a long
time ago that actually light is - little
particles called corpuscles but that
doesn't explain some of the wave
properties we have light diffraction and
refraction and in 1901 so just over 100
years ago we had Matt Planck part of the
work that Matt Planck looked at was what
we called blackbody radiation and this
is the kind of blackbody radiation curve
we might have emitted by an object and
there's a link during the energy and the
wavelength and what he theorized was
that radiation is emitted in discrete
packets of energy and this is a what was
known as quanta so we basically quanta
sized the energy into small discrete
layers and he then looked at the energy
of each quantum of energy so the
smallest unit of energy he might have
had and what he said that there is a
link between the energy and the
frequency and this link between the two
of them when it must be a constant here
which is what is called Planck's
constant so E is equal to HF but that
wasn't exactly the photon okay this was
just saying that a link between the
energy emitted and the frequency of that
emitted radiation but it was four years
later in about 1985 that Einstein really
ever published his work on the idea that
energy isn't just emitted in discrete
packet of energy but it actually
continues and this concentrated packet
of energy has particle-like properties
sometimes given a symbol a bit like this
to share that it's a a discrete little
packet of energy and this is what is
called a photon here we have a rather
badly drawn picture of the e/m spectrum
which you've already had a few videos
about and what we find is that we have
waves as we think about them going from
radio waves at one end through to gamma
at the other
so the idea that Ison really came up
with is that energy exists in these
discrete packets of quanta and we maybe
had the low energy photons at one end
moving through the the higher and higher
energies the visible light going from
red through to violet then the
ultraviolet which is more energetic
there's more energy in an x-ray photon
and finally the gamma ray photons are
the most energetic of all and that's
because these have the highest frequency
waves and therefore they might have the
most highly energetic photons so what
else do we know about these photons well
we you know we know certain things
perhaps if you have maybe three photons
combining together that does effectively
give us the white light for example
which is a word that have the white
light in the spectrum down here also the
things about the photons that we need to
know is that they are massless okay so
they have no mass or their rest mass is
equal to zero and what that means is
that they therefore travel at the speed
of light or an actual fact they can only
travel at the speed of light anything
that has no mass only travels at the
speed of light for example some of the
exchange particles where in which case
the photon is one of those and anything
which does have masks and can never get
to the speed of light what else about it
well we already know that e is equal to
hf and we know from previous work that
the speed is equal to F lambda so we can
combine these two equations to also say
that the energy is equal to HC over
lambda so we can look at the fact that
these massless particles travel at the
speed of light and we can look at the
energy if we know about what Planck's
constant is and then if we have some the
other kind of wave-like properties at
the time so these photons are pretty
amazing these tiny particles are lighter
which there are billions and billions
traveling around all over the place they
allow us to look at certain effects that
the wave properties of radiation don't
allow us to really kind of fully
understand and you know there are
certain things which are amazing for
example when you see the stars at night
a photon must have been emitted by that
star maybe millions of years ago and the
first thing it's actually hit after
traveling through space for maybe
millions and millions of years it's the
back of your eye where that little
bundle of energy that little pack
of energy has caused a signal to go down
your brain or down the optic nerve into
your brain chatter you let you see that
star which is out there so these are
pretty amazing things and it's one of
the ways that we can actually model the
world