An experiment demonstrating the total internal reflection of light inside a glass block. An angular scale is provided allowing the critical angle of the glass to be measured and the refractive index of the glass to be determined.
As a physics tutor, I've found this video to be very useful. Many professors do not perform an in class demonstration of critical angles, leading many students to not understand critical angles and think of it as an abstract topic. Showing them video has contiually been the easiest way to help them understand. Thank you for a simple video
Is there anyway you can describe what's happening & how it is used w/o putting yourself out? If not thanks. I'm fascinated by light, physics & geometry. I lack the education though.
@@wellrose17 in this video, total internal refraction of light is being demonstrated. When light enters from optically rarer medium (air) to optically denser medium (glass slab) it bends towards the normal. When light travels from optically denser medium ( glass slab) to a optically rarer medium (air) it bends away from the normal. This case is required in TIR. When the angle between the incident ray and the normal becomes greater than the critical angle, TIR occurs. What is critical angle? Critical angle is the angle where the refractive angle becomes 90°, which means that when light is refracted going from denser to rarer medium, it's seen as grazing emergence ( refracted ray passes through the normal )
@@wellrose17 If you want a simpler explanation, you notice those angle markings? When the angle at which the light hits the glass is lower than around 42°, it's slightly bent, which is shown in the beginning of the video. When it is at exactly 42° (the critical angle), the light is dispersed, forming a spectrum (the rainbow stuff you see around 0:56). After that, when the angle is higher than 42°,the light is instead reflected, which is the Total Internal Reflection in the title of the video. If you want specifics, the dude above me did it pretty damn well.
0:56 Here he crossed the Critical Angle of glass that is 42°. At this point, the refracted ray is along the glass-air interface. After crossing that angle, no refraction occurs and only reflection takes place :)
Refractive index of glass is about 1.52. However, after applying formula of refractive index (sin i/sin r, included that the critical angle of glass is 42°), the result is about 1.49. So, a better representation for the critical angle of glass would be 41°, because when applied it is about 1.52 (or closer anyway).
A teacher once asked me what can be learned from silence then immediately said nothing can be learned. And just now by the sound of silence ive learned more than that teacher ever taught me.
@@silentHunter123 did you not even fully read my comment? I already said it was dispersion! And yes, I already know that the the refraction, reflection and refraction again, of light through two materials that have a different refractive index and are at different angles relative to the direction of travel of light, will separate light into its constituent visible colors! XD
@@ivanshuyadav566 well, actually I'm not very upset, I just thought it was hilarious that somebody could be so blind when commenting. 😂 (no offence Shashwat Saxena)
The light source is a standard school ray box. If you're after a similar source I would actually recommend using a laser spirit level - they produce much brighter beams and can be bought fairly cheaply from most DIY stores!
Everybody can actually observe Total internal refraction by opening their eyes underwater and looking up to the surface of the water. (Either in the ocean, but also a larger bath tub will work.) You will typically see: 1: A central, circular area which forms at the water surface and in which you may directly observe the surroundings above the water surface (e.g. the sky). In the video, this corresponds to the light ray exiting the glass. 2: Outside of that central spot however, the underwater enviroment is mirrored. (In dark underwater enviroments this part of the water surface is often darker or even black. In a bathtub or any really bright enviroment however, this might take on more the appereance of a bright mirror image.) So the angle at which that circle sits indicates the angle of total internal refraction. (And of course it is not a perfect circle, but quite distorted by waves.) This explains the typical look of underwater images facing up to the surface.
This is the first time I got actual feel of Total Internal Reflection I really appreciate this video,,,and would love to see more such phenomena practically
I honestly did not get a goddamn thing from my lessons on reflection. So uninteresting. And that's from the guy who read the textbooks for fun a bit ago.
PERFECT demonstration !! From refraction to total internal reflection, once critical angle is passed.. + a look at how reflection already happens to a small extent just before achieving i=C. TQ !! 👍🏻👍🏻
[2023-11-11] We did this experiment in my 8th-grade (Jr. High) "Light" class almost a half-century ago (c. 1974). We had to observe and collect data of the exiting light's refraction angle at various angles of incidence into the glass block and determine at which angle of incidence, the light was internally reflected by the straight face of the block-scientific ideas on the properties of light, being introduced to 13-year-olds. Fascinating that the light apparatus hasn't changed in all those years. The screen in the apparatus can be inserted upside down (with the 3-slit side down) which would allow us to see the interference pattern of light emanating from the apparatus (demonstrating the wave properties of light). You can also see the interference in the lone beam emanating from the apparatus, as light tries to spill, at various intensity, either side of the primary beam.
Excellent, as a student gemmologist, I find that this is an excellent video for studying refraction and Total Internal Reflection (TIR). Towards the end of the video, you were going towards the critical angle, where the angle of incidence is at such an angle that the angle of reflection is both reflecting and refracting along the optically dense media. Thank you for the superb video, I would definitely recommend it to my fellow student gemmologists.
One of the best video I've seen in RU-vid in my life, If we don't use these amazing videos to educate students, this digital world would be a waste This is called the real learning. Thank you for this magnificent video
I LOVE THIS VIDEO. AS A GRADUATE GEMOLOGIST I USE TOTAL INTERNAL REFLECTION WHEN I TAKE REFRACTIVE INDEX READINGS AS PART OF THE PROCESS OF IDENTIFYING A GEMSTONE. BIG FUN!
@@urzsulaz2604 A standard, good quality gemological refractometer is what is used. There are several videos available on RU-vid that provide information on how to use it.
Such a beautiful demonstration. I wish physics teacher actually showed us experiments rather than being worried about quickly completing syllabus. I think nothing can match the clarity that experiments provide. First the experiment should be demonstrated and then from their we should connect it to the theory That will make physics a better experience for most students
Perfect Video. no Music NO inane commentary something a half decent teacher in a mud hut in the middle of Africa could use to demonstrate he concepts involved. at my school we had the equipment, but videos like this mean that NO Pupil in the world needs to be ‘deprived” more please.
I've been watching professor Julius Sumner and his demonstrations of physics peaks my interest into the subject. It's demonstrations like these that get me excited to learn. Thanks for the vid.
Never seen such a beautiful way of explaining this concept...it was not only interesting to watch it happening live but quite useful to understand the theoretical concept easily 👍... great work 👍
Physics tell us how our universe work, real demonstration should be in daily school learning to make student more understanding the basic concept of physics
Glad this is finally practical! So happy to see that this isn't some abstract topic we learn in class and that's that. Happy to see it exists for real and isn't just another theory
Most people will know this phenomenon from *being underwater* (in a pool) -look up to the surface and you can't see past the surface -all the light is reflected internally. UNTIL you get close to the surface, pass the critical angle, and suddenly look up and you can see the sky.
Wow amazing - I studied that in physics 30 years ago and loved it but now I love it more after watching this video - I like the rainbow near the end of this video
Love this man.... You cleared all my doubts of geometric optics in just 1:43 min... 😍😍😍😍😍 A fan of your and your kind work..... Please keep helping student like me....... Love from india....
thank you for the video sir it really explains about the critical angle and the internal reflection phenomenon of the light... these days having observation like this physically is not possible.. cuz people don't give enough effort or time to do these ... this video really creats better understanding..
@@ganges2264 Just like light, fluids are made of waves and particles. Everything around us that we see is made of fluids and non-fluids(solid). Light should fall in fluids because we know for sure it isn't a solid but that isn't enough. Light flows in straight line, any fluid that flows in extreme high speed, will flow in a straight line so light can be a fluid.
@@Vetrivel.Shanmugam ah thanks for telling me. However it's very hard to determine light as a fluid considering it breaks so many of the fundamental laws about fluid. Light can be bent , it can be reflected , it can physically pass through transparent objects and it can be warped when around blackholes. I think there are other ways to classify this bcs light is the only thing in the universe that doesn't have mass , which fluids fundamentally need.
@@ganges2264 Thanks, one more important thing I forgot to put it. Just like fluids, light flows, and it flows parallel inbetween spaces. blackholes doesn't bend light, it bends the space whereas light simply flows through the bent space. Light has mass, its mass element is called photon.
Towards the critical angle, the light actually started getting dispersed into a rainbow. So that's why they mostly give us a monochromatic light in questions regarding refraction!
n * sin (a) = n * sin (b) 1 * 1 = n * sin (42 +-1) 1/sin (42 +-1) = n (asuming that everything is correct, the light beam is monochromatic (even though we can see that it is not), n of the air is 1, a = 90º and b = 42º) n = 1,49447... (n ~ 1,5) whith that +-1º of error n of the glass is between 1,5243 (41º) and 1,4662 (43º)
Thanks a lot sir! All of your videos are really helpful! Sir please make a video demonstrating a difference between virtual and real image! Please sir! This would be a great help for me! Hope you'll help!
This is so satisfying to watch😍😍 Amazing, I had no idea about what is TIR, it was so boring learning the topic from the book after watching this video I clearly understood what actually TIR is thank you so much☺☺🤗🤗
Lessons will be more fun and interactive if these experiments are done in class. Students will also develop an interest in the subject. Unfortunately, teachers just keep loading childrens' brain with theory only.
I fully agree! Experiments are not only the most fun part of science, but also the most important part. It’s through experimentation that we learn about the world, discovering and confirming the theory taught in the classroom.
This is an amazing!! I would like to make a demonstration for my children. Could you please let me know what light source you used for this, and how you made the housing for the light source?
The light source housing was bought from an educational seller, but a suitable set up could easily be constructed using a 12v bulb and some cardboard (be careful if the bulb gets hot thought. To be frank, though, the best way to do the experiment is to use a laser pointer instead of a bulb. They can be purchased for very little money and are very bright.
Well if you had the internet connection during class it could have heard it, you also could have searched for the topic on google or if your google account is connected with social media like facebook or something then the friends you have could have searched for the topic on google. It's all connected... quite scary.
I have my physics boards tomorrow. This total internal reflection concept is included. Though I watched this video 5 to 6 times before I returned to one last time before my exams
@@samoriginal yes. Here is how it occurred to me. There are only two forms of matter that we can visually see. Fluids and non-fluids(solids). Though we can say straight forward that we know for sure light is not a solid, it can be a fluid is not enough. So digging into more properties of light we have. Light is both a particle and a wave. A Fluid is both a particle and has wave on disturbance. Light travels in straight line. A fluid can travel in a straight line at high speed. Light travels in high speed and in straight line similar to fluid.
my teacher did that too and it was so dumb we never understood anything she just told us to look at pins from inside the slab and mark where we put the pins and hand it over to her and nobody understood a single fucking thing and then she started insulting us about how we are dumb. a total waste.
