Total Internal Reflection - Sixty Symbols

[danjoelabrenica]

i hate my school but i love this channel :D

[PeidoLord]

Does whether or not the waves get totally internally reflected depend on the relative densities of the materials?

[njimko23]

@PeidoLord - Snell's law gives the exit angle as a function of the ratio of indexes of refraction and also the angle of incidence. If the exit angle is greater than 90 degrees from normal, then the waves cannot go through and instead reflect.

I think the skipping over the air gap is because the microwaves set up areas of charge in the paraffin, and that induces a charge on the other side of the gap. That is a classical rather than specifically a quantum effect.

[jagara1]

Please please - can you give us an explanation for what is actually happening...

[BULLBRANDDAN]

Is this because of Quantum Tunnelling?

[xanshriekal]

For a man who claims to not be an experimentalist, he sure does a lot of demos for us. :)

[chan625]

I liked the other vids but this one just ended with a question it asked!

[Vermin298]

why isnt there more stuff like this on tv? am i part of a minority that likes interesting sciency things?

[johncrwarner]

Is there a need to invoke QED to explain this - as the idea that a wave knows anything seems far to anthropomorphic for my taste - I have a feeling that there must be some probability of the photon being detected in different places. The second prism is thus changing the probabilities.

[watchmikereedy]

I have a question. Imagine an object that is half a sphere, hollow on the inside. The outer edge is non reflective while the inside is 100% reflective. If this object was brought together with another object of it's exact likeness, similar to 2 halves of a coconut being brought together to form the full coconut, would the inside be completely dark or would it reflect the last image(s) of light shown on the inside?

[juggaloryan3]

@watchmikereedy completely dark. the light gets lost as heat energy

[kokopelli314]

To expand a bit on what @diedy5 said, if the wavelength were shorter then the prisms would have to be closer together to cancel internal reflection and could be further apart with a longer wavelength. Although the wave is reflected in a prism, part of the wave or a probability of the photon exists beyond the face of the prism. Reflection breaks down when the portion of the wave inside the second prism is greater than the gap.

[duguder]

Since it bounce of the second face of the first, would it be logical to assume it would bounce of the second face of the second prizm?

[GammahooX]

It goes through because the photons are quantum tunneling through the gap.

[cosmiceon]

sticky back plastic? dont you mean tape??

[wigleypg]

The wave is evanescent at the interface - its extends beyond the interface but bounces because it can't propagate through (can't satisfy the boundary conditions of Maxwell's equation at that interface). When the second prism is brought close to the first the wave can cross the boundary because the conditions are satisfied. In essence the boundary ceases to exist (or becomes very small compared to a wavelength) and so the wave passes straight through.

[JLConawayII]

I'm going to log this one away under "quantum voodoo"

[climatixseuche]

please can you explain WHY?

I mean, I wondering if the wave has eyes and can see the 2nd prisma ^_^

[Skindoggiedog]

He doesn't actually explain it ... just shows you it in action. Anybody could do that.

What people want to know is WHY.

[joshuafrye182]

I've never heard tape called 'sticky back plastic'.

[chrisofnottingham]

I have a suspicion that the full explanation of this involves QM and that crazy thing where the wave takes all possible paths simultaneously but they all cancel out apart from the one path we see it take. Is this along the right lines?

[wheetman]

Read QED by Richard Feynman and all will be explained... well read it twice and drink some mushroom tea and meditate in absolute silence for 3 days and then you'll be ready for understanding to wonderful world of Quantum Electrodynamics!

[harry3life]

OMG I cannot stop watching these videos, so interesting, I only have 4 hours of sleep left before school

[Magnum756]

this is [cool]^2

[FelipeZucchetti]

amazing....i didn't know this about water...many thanks...if you want, check out some of my experiments on my channel...thanks for share knowledge...

[HaT223]

The reason the wave reflects when thier is no 2nd prisim is because there is a change of medium(from wax to air) and refraction or internal reflection only happens when there is a change in meduim. When the second prisim moves in No recflection occurs in the middle of prisim as it is continous meduim and at the end the wave just bends a little like professor suggested.

[harmonicgrunt]

Did it transmit through beacause 2nd prism ((Exit)) is Parallel to transmit interface?.

Flatface To Flat Face?. Awesome Video By the Way.☺

[WalneyCol]

"somehow"?

[gremlindude10]

i lost marks in a physics test for saying bouncing instead of internally reflecting.

[mesobored123]

Total internal reflection is when a light from a higher refractive index goes to a lower one at an specific angle or higher. Because the shavings have a higher refractive index than the air and the angle is positioned in such a way there was a total internal refraction. But when the 2nd box is introduced the refraction index is basically unchanged so it would just pass right on though and when it will not bounce because the angle is changed.

[unknotmiguel]

but when it bounces off in the first prism to the other face of the prism, why it penetrates through and not bounce again??

[BuggttiVeyronW16]

Can someone explain this Total Internal Reflection effect to me a bit more specificly? I am very amused by the cool effect but at the same time very confused by the laws or explaination that allows this to happen. So can someone who's very good at this to explain this to me, please? Thx.

[Twist9]

NUTS! Way crazy! I love this kind of science, just completely goes against common sense yet we know somewhat how it works, brilliant!

[joel4692]

No, no, no, @BGenerous & @Envergure remember he said the wavelength of the microwave in question is about 3 cm. This means that when you bring the "prisms" within about a centimeter, the radiation sees the two separate boxes of paraffin pellets as one! The cardboard is always transparent, the microwave radiation was just bouncing off the border of pellets/air.

[eltotoX]

That was pretty awesome, but I'd like for him to elaborate on the part where he said '/somehow/ leaks through this region' at the very end. I wonder what that 'somehow' means.

Also, we need a George interview!

[sixtysymbols]

@eltotoX:

Interview with George (along with the elusive Neil from periodicvideos) coming soon...

Will probably be posted to our nottinghamscience channel, so keep an eye on it (or better yet, subscribe)!

That's where we put all our extra behind-the-scenes stuff...

[unxzst]

"somehow" he said it satisfies the boundary condition. what that means i'm not sure, but i know waves (of particles) will be detected on the other side of a barrier, if the wavelength is larger than the barrier.

[eltotoX]

What I'm curious about is that if the big cardboard prism is all by itself, the thing reflects the waves, but if there is another prism CLOSE to it, the wave 'sees' them as being one.

Now, somehow the wave 'knows' beforehand where to go. It can't go past a prism and say "oh there wasn't another prism here so I'll just go back in time and reflect". How does this work?

[robertwc82]

all i can tell you is the universe is a strange, strange place

[Focusb4ufire]

@eltotoX I dont know the answer but heres an guess (im a biologist not a physicist) he said the waves are 3cm long, hence because you have altered the exit angel of the cardboard, the angle makes it impossible for the 3cm waves to jump the cardboard at that point, and so is instead reflected. Think of lightning, it goes for the path of least resistance. only when you put more parafin there by joining the other triangle does it become less resistant than the alternatives.

[Grundalizer]

@eltotoX QED by Richard Feynman

[dragonology294]

@eltotoX Is George the "Einstein" guy? coz i like how he explain things..

[Daemonique]

@eltotoX The "somehow" works the following way: he already explained that to the microwave beam, the paraffin particles seem as a continuous medium since they're very much smaller than the wavelength of 3 cm. When he brings the 2nd "prism" close to the 1st, the distance is also much shorter than 3 cm and so the microwaves go right through without detecting the bit of cardboard in between.

[BlueCollarScience]

Bragg scattering ?

[v4lgrind]

Great show. Now more details please.

[panchoxpanchox]

waves go in 4 dimensions... that's what happens

[Envergure]

Awesome! I gotta get me one of them microwave generators! Is the cardboard "transparent" as well, or is the radiation skipping over it because it's so thin? Is "sticky-back plastic" the same thing as adhesive tape?

[BGenerous]

I think the cardboard is transparent. That's why you can microwave food that comes in cardboard boxes.

[ofcata]

Thank you, that was amazing!

[TheCynicalAtheist]

You guys should do the one with the water tanks and a light under the water reflected back from the interface.

Doing the slit experiments would be awesome too.

[TheBentastic]

George is AWESOME

[G3org3Master]

I am.

[culwin]

Whoa...

[trunkszetto]

I know these videos are made to be watched by the average viewer (ie one lacking in physics education), but even having taken physics courses I tend to get something new from an SS video.

I vaguely remember the concepts of index of refraction and Snell's Law from courses, but they don't go too in-depth about it here. I'm surprised he didn't tie it in with the previous demonstrations they'd done on fiber optics.

Great video as usual, but I wish it had a bit more on the topic.

[steadfast1984]

very interesting. for some reason i like these dry intellectual videos a lot.

[TheJapanChannelDcom]

Refreshing change to see intelligent stuff on youtube!

[zeratul575]

aint there a danger of having your hand right infront of that microwave prodouser thingy?

cuz im worried for the guy

[TheCynicalAtheist]

Not really, they will be low power, you are surrounded by microwaves right now.

The sun, the cosmos, your wifi, your mobile phone your bluetooth etc, all giving out microwaves.

[Doogeedoo12]

Doesn't this have to do with the transfer of the wave into a more/less dense medium? The microwaves go through the 2nd prism because the medium doesn't actually change. At least, this is what I am to believe.

[redone632]

Good video. I would of hoped for more explanation on the angles and such. I still am not quite convinced.

[goldenc88]

For total internal reflection, there is an equation you use to determine the angle:

sin theta = n2/n1 where n2 is the medium the light is traveling through (usually air, where n = approx 1) and n1 is the index of refraction for the prism (for glass prisms usually 1.45 or 1.5 - let's use 1.45.)

Therefore, theta = sin^-1 (1/1.45) = 43.6 - this is the angle to perpendicular. Double it and get 87.2 degrees, which is the angle you put the prism edge to make total internal reflection (when n=1.45.)

[goldenc88]

Sorry, the 43.6 is the angle you put the edge, the light bounces at 87.2 degrees.

[goldenc88]

Rewatching the video, the angle it reflects is beyond 90 degrees, so my best guess is that his prism has an index of refraction of 1.35, which would create a bouncing angle of 95.6 degrees.

[holon67]

does hegel cover this topic?

[seanbrockest]

George made that laser? It looks like a Black and Decker Leveling Laster (available at your local home building store, buy one today!)

[stupidguyaabbcc]

Physics > Math :D

I know they go hand-in-hand

[jtdreisb]

Actually

math ⊂ physics

[BeortheMad]

Mhmm, How does the wave know there is another "prisma" close enough for it to go straight ahead? I don't really understand how the 2nd "prisma" getting closer can effect the wave that would bounce off. Do waves "check" the space ahead of them in order to decide what to do?

My none-scientific mind is really confused now :D

[FnordPerfect]

I thought the same thing, it's both confusing and amazing.

[clarkcolt45]

non locality and the wave function.. eh, just kidding :D

[harry3life]

@BeortheMad

I think it has to do with "refraction". if light or waves want to continue to go through the object at a particular angle it has to refract. now it sometimes cant refract and bounces off, but if there is an object behind it with the same or similair refraction index it doesnt need to refract and can pass through it

[diedy5]

@BeortheMad You can compare the 2 prisms to two of those white marbles. There is space between everything. The waves will just take the easiest way, they don't check what way is easier it just happens (think of water) when the second prism gets close enough it will start moving at the new direction which has less resistance. You just need to understand resistance. It will move in all ways but since one way is so much better then the rest mainstream will move in that direction.

[holsson85]

So cool!

[leporidus]

The microwave-parafin-wax experiment is a wonderful and surprising demonstration of total reflection and propagation of waves through a medium.

The cardboard "gap" just doesn't exist for the microwaves, because their resolution is not high enough to "see" the gap. I love it!

[GeeKayKayGee]

SixtySymbols is a wonderful project and I hope that you'll have many many more episodes coming down the pipe.

[sixtysymbols]

@GeeKayKayGee: We've got the nod to do another sixty, so we should be going for a while yet! Filmed some cool stuff about stars, the 4th dimension and supernovae today!

[insAneTunA]

Awesome !!! I like good old Albert Einstein.

[GeeKayKayGee]

Another 60 episodes to come?

"This is most excellent news. I like most this news. Bring me some better news, you could not."

Science for the win, this really is news that brightens my day. Thanks for all you've done so far SixtySymbols and thanks for all you've got to come.

[TheCynicalAtheist]

Oh shit i just had a nerdgasm.

Thank you guys so much and keep up the good work.

[ReverendFlatus]

@sixtysymbols In that case maybe you should change your name to onehundredandtwentysymbols! I agree with eltotoX, I'd like a better explanation, I'm not sure I completely understand what's happening.

[afhdfh]

That's awesome! Though I really don't get it at all. ;)

[farhmoha]

Yea it stopped towards the end for me.

[enkylling]

awsome

[sixtysymbols]

Apologies for second upload... The original contained a problem that was not our fault causing it stop near the end!

[Mocktails]

IT'S OKAY :)

[LatumWay]

It stopped about half way through for me. But this one it working.

[Forssa1]

Doesn't  load at all for me... I think something is wrong on youtube's side.

[DeathlyCrunch]

It's been happening for me with a lot of videos as well :S

Not sure if it's a FireFox problem or YouTube is messing around with it;'s servers.