Okay, here we are. This is Mr. Masley here with a special IB physics video lecture
in Minecraft. In this lecture I'm specifically going
to be using Minecraft to explain diffraction and Huygen's Principle. And
while this is definitely 100% just a gimmick. Huygen's Principle and
diffraction actually works very well in Minecraft because the Minecraft water
actually obeys Huygens principle perfectly, and it makes a pretty good
demo of what I'm trying to explain when I talk about Huygens Principle. So just
as a quick reminder Huygens principle is the idea that every point of an
advancing wavefront is a new center of disturbance from which emanate
independent waves in all directions. So what this means is if you have a wave
moving from left to right, as is the case in the wavefront displayed here, each
individual point on any line in that wavefront is behaving like a center of
disturbance with waves emanating out from that center of disturbance in all
directions. So what this means is I can pick any one point on that wavefront
and it will behave like a single center of disturbance with a kind of circular
wave emanating out in all directions. And the reason why this works is that if I
line up all the points like this, you can see that the area of overlap that all
the waves share is right here, so this is where the next line of the wavefront
occurs, and you can see that that's true, but this can be a little abstract and
Minecraft can actually help us with this because the Minecraft water actually
obeys Huygens principle. what I mean when I say that the Minecraft water obeys
Huygens principle is that any one individual block of water acts as a
center of disturbance where water is emanating from it in all directions like
this, so this is obviously not actually a wave, this is just water emanating out
until it kind of dissipates into nothing. So it's not exactly the same, but it's
close enough that similar properties are observed. So any one water tile emanates
water outward in all directions like this because water tiles emanate water
outward like that in all directions. If you line up multiple water tiles
you'll notice that the parts that I lined up are kind of adding together
they're constructively interfering with each other. So instead of one single dot
emanating out in all directions, when they're interfering with each other they
create this pattern where all the water is kind of moving in one direction in
that way. And if I continue to line them up, each individual point of water is
acting as a center of disturbance, but because they're all lined up like this,
just like centers of disturbances are in a wavefront, all the water kind of moves
in one direction that way, so this is behaving like a single wave moving in
one very specific direction rather than a bunch of individual points all
radiating outward in all directions. But in truth they're basically the same
thing, because the individual points are interfering with each other to create
this total pattern. So that's what Huygens principle is saying, it's saying
that this one total wave moving in this one direction can actually be modeled as
a bunch of individual centers of disturbance, where the water is radiating
outward in every direction. And because of the interference it behaves like one
big wave even though these are all actually centers of disturbance.
One thing that I'm extra excited about with the Minecraft water is that because
it obeys Huygens principle, the diffraction patterns that occur when it
encounters a barrier are actually the same that occur when waves encounter a
barrier. So for example we've got all this water lined up here and it's
encountering a barrier right here, it can't get through. So the idea is that
this water is kind of behaving as one large wave moving forward and impacting
a barrier here, and so if I make a small opening in the barrier diffraction is
going to occur, and it would occur in the way that we would expect it to for a
single slit. So I opened it up for a single slit and you can see that it's
occurring basically as we would predict it. So for a single slit we have this
full wave impacting the boundary, and after it spreads out in all directions
leaving the boundary. So this is what we mean when we talk about diffraction: the
single wave spreading outwards in all direction after it exits a small opening
in a barrier. We can also observe the pattern for a multi-slit experiment. So
I'm going to open up a few more, and I can see that because of the interference
pattern there are certain places where these waves are constructively
interfering with each other to create a slightly different pattern than we've
seen before. So this is the image for a multi slit experiment. And again this
obviously is a little bit different as well, because with an actual wave there
would be points of destructive interference as well, and the Minecraft
water can't model that but it still gives you an idea of what Huygens
principle is saying, because each of these individual points of water is
behaving as a center of disturbance where water radiates outward in all
directions. That's why we see the pattern that we do when waves encounter a
boundary. Finally, we can just completely remove the boundary, and if we completely
remove it we can see that we now have a single overall wave where each
individual point is behaving as a center of disturbance.
So that's a way that you can use the Minecraft water to understand
Huygens principle.