What is Polarised Light? (Polarisation Part 1 - Waves - Physics)
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- čas přidán 20. 07. 2024
- Light can be Polarised. What does it mean? In this video, I use the wave representation of light to explain what makes a ray of light polarised. Then, I propose a description of what is unpolarised light. After this, I explain how unpolarised light can be polarised using a Polariser.
This does not only apply to light. Mechanical (transversal) waves can be polarised too. To demonstrate that, I improvise an experiment with what I find in my house…
And what about when the incident light entering a polariser is already polarised. I show you on the white board the effect of the polariser on the amplitude and plane of oscillation of the light.
This last section will be the starting point for the next episode, where I will derive and show you how to apply Malus’ law. Malus' law deals with how a Polariser modifies the energy carried by light.
The video is concluded in an example of what could be answered at the exam question: “define what is polarised light”.
00:15 What is polarised light?
01:53 What is unpolarised light?
02:50 Effect of a polariser on unpolarised light.
03:45 Polarisation of a mechanical wave (demonstration).
05:54 Effect of a Polariser of incident polarised light.
07:30 What is polarised light? What to answer at an exam?
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This video is produced and presented by Edouard Reny, Ph.D. in solid state chemistry and private tutor in Physical Sciences.
For access to great resources that will help you with your studies of high school Physics, visit and subscribe to the "Physics Made Easy" website:
www.physics-made-easy.com/
Edouard provides one-on-one private tuition in Physics (face to face or by Skype). If you wish to contact him, visit his website: www.physics-tutor.nl/
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Im impressed, your the only perso who explained it in a way that made sense. Tyvm
honestly🤣
Using the oven rack and the bass guitar cable was a great way to visualize it and make it memorable. Thank you!
So that’s one concept you will not have trouble remembering. Goal Achieved !
This channel has saved me hours of headache. I salute you sir for doing this amazing job and providing all of this education for free.
Hell Sas, you are welcome, and I am glad I could avoid you headaches! As I told another viewer, providing these videos is my little contribution (I feel gratitude, so I enjoy paying back some of the gifts nature gave me)
Sir I have seen many videos of urs... omg what an explanation... seriously u are doing a great job making our life easier sir... thanks a lot..
Thank you very much Krithika for your encouragements!
This is really a time saving video.... didn't regret clicking....
Really appreciate the time you do for these videos, best teacher on CZcams by far. I've been looking for the explanations of magnetic and electric fields, and after many videos trying to explain it, you were the only one breaking it down and really explained it.
Wow, thank you Karl for this really kind comment! *** Blush*** It really motivates me to produce more videos like this one. I am glad to have improved your understanding of electric and magnetic fields. Maybe you can try the videos that didn't hit it at first and see if they appear clearer now.
Really appreciate your videos. You have a good way of explaining things. Much respect
Thank you D. That's why I am teacher :-)!
I like how you used everyday objects to demonstrate :)
Studying with visualisation here😍.. thanks sir..
Good stuff. Presented clearly and thoroughly. Not only illuminating in terms of polarised light....but heck! Never conciously occured to me that unpolorised light waves oscillate (I guess) in all directions simultaneously. (will have to watch more of your videos to get a better grasp on that : )
Thanks Sailor! You seem to like sailing. Try that:
Buy yourself a polariser (like a polarising filter for phorography). When you enjoying your freedom sailing at sea under a a shiny sun, look at the flickering reflections of the sunlight on the water waves. Then look under the polariser, and rotate it. You will see some of these reflection disappear. Welcome to the world of Brewster's angle!
Everything is very clearly explained and illustrated, so impressing 🙏🙏
Thank you for your kind words Ageu!
Best explanation on CZcams. Liked and subscribed
Hi Puniyani, thank you for your words of encouragement! ❤
excellent video! such a simple, yet informative explanation!
Thank you Aisha for your kind words :-)
I agree with the top liked comment here, I've gone through a few videos looking for an to understand explanation and you were the only one I found until now who could give it, so thank you very much!
Merci Arnaud, I am glad my videos clarified things for you :-)!
Amazing video amazing all around thank you the guitar cameo was great! Such excellent material that makes things intuitive and learning deeply
Thank you Nimisha! How's your one-man show initiative going? I haven't seen any new video on your channel :-(
Its really an interesting video, sir. You made physics easy. "Physics made easy".
Excellent explanation and demonstration. Kudos!
Thank you for kind word and encouragment!
Wonderful explanation you are a great teacher. Loved your video to core of my brain.
Thank you Hakeem,. I am glad you enjoy my work!
Such a great and fun explanation !!
Thank you :)
Thank you so much for this video, I found it very easy to understand
This was a great explanation subscription earned!
I am glad you enjoyed my work! Welcome to Physics Made Easy :-)!
Very nice explination ❤️. Amazing video
thanks sir..... your way of of teaching is super duper
I love your explanation, thanks alot!!
You are welcome Moritz :-)
Excellent Information
i saw the intro and knew it was gonna be a great video, thank you :-)
Glad you liked it!
I can not find a world to describe your power of teaching,
They say, the knowledge is power and I would say, your power of teaching is only comparable with the power of sun ☀️
A million thanks for being out there for physics lovers. ❤️❤️
Wow thank you Sam, for these very encouraging words! I do not know if my power of teaching is 4 x 10^26 Watts, haha, but if it can help students to avoid the pain I went through when I was a student, that is enough to make me happy!
Wonderful explanation, simple but accurate. Thanks.
Thank you for your kind words Minh!
Wow. Great explanation
Merci Elorm, I am glad if the video helped you understand Polarisation!
Great sir...
I usually don't leave a comment but man! this video compelled me to do so. Thank you for this..
You are welcome Manav, I am glad you enjoyed my work :-)!
Fantastic explanation - especially the oven rack! 😀
haha, yes it's always a lot of fun walking around the house wondering what to use out of my everyday stuff to help at the visualization of a concept. I was pretty proud of the idea of the oven rack to polarize a mechanical wave :-).
You are a living legend ❤️
Awesome 👌
Excellent
Really good video. Thanks.
Superb explanation and demonstration. Subscribed.
Thank you , and I am glad you enjoyed my work :-)
You made it easy! Thank you!
Hey Andres, I am glad it helped you!
good man! thanks. very good vid and super helpful explanation. keep it up!
Thank you Harlan for the encouragement!
You're the best 🌟
Awesome video thank you!
You are welcome Roma :-) I am glad you enjoyed it.
Thanks, Sir, for this markable effort!
You are welcome Jassim. I hope my videos help you in physics!
Clearly explained.. Great video.
Thank you Edro, I am glad you enjoyed it!
great explanation professor thanks a lot.
You are welcome Tamer!
OMG, OMG, OMG. What a wonderful video!!! Thank you, sir!!!
Hi, you are warmly welcome. I am glad you enjoyed my work!
Thank you so much for the video, I finally understood what is a plane-polarised light the day before my physics exam! They should replace all the texts in the book with this video!
Merci Shual. My video replacing text books, maybe not haha! But seeing it at as a good complement, or starting point, yes. The idea with my videos is to read the text book after seeing the video: the goal is to provide a basis of conceptual understanding so that the viewer can dig deeper by himself.
The video editing is amazing
Thank you so much, it is the most time consuming part of producing the video: I am glad you enjoyed it.
Amazing sir. Thanks for using your oven and guitar
My oven and my (bass) guitar let you know that you are welcome :-)
i am so glad that you made this vedio. honestly it has helped alot😊
Thank you Muneeb
i love this so much very well explained!!
Thank you Khadija
Physics in simplicity is just awesome！
I fully agree, that is why I do what I do ;-)
Congratulations, you did a great job in explaining the matter, an the example with the rack was brilliant. I have a question, maybe you can enlighten me. Based on my current understanding, one lens of the polarizing 3D glasses will allow the vertical polarized light to pass and the other one will allow the horizontal one. I tried to put one above the other, hoping to filter out most of the light. However, this did not happen, how should I understand this ?
If these are basic polarizing 3D glasses, all light should be stopped. But, maybe modern ones have a different way of working: there is some electronics in them that actually is synced to a signal that can make the polarisation axes of each lens flip in synchronicity with the movie...If this is true: the axis of pol between left and right may not necessarily be perpendicular in the absence of a sync signal. I am only speculating there... and I might be completely wrong, so you should check this by yourself on the web.
Best explanation on the net.
Thank you :-)
@@PhysicsMadeEasy Thank you!
Thanks for this :)
Thank you!
Wow I understood every step... Simplicity is the best way for me, some ppl speak so mechanical they lose you in just hearing the syllables in the words you don't understand😩
Hey. Thank you. I am glad you enjoyed the video.
That was a great explanation. For a polarized light why do we only talk about the electric field oscilating in one plane and not about the magetic field??
According to Maxwell equations, a fluctuation of E in space, generates a fluctuation of B in time (and vice versa) perpendicular to the plane where the electric field fluctuates. Therefore, one implies the other. The origin is actually the electric field, the magnetic field being just a consequence of special relativity. When we talk about one, we imply the other. So for simplicity, when discussing linear polarization at the level of the video, it is not really necessary to discuss the magnetic field. the latter is implied.
This is very simplified and understandable❤
I try to make Physics Easy while keeping things rigorous. Thank you for letting me know it works :-)!
I enjoyed watching.
Nice!
Excellent 😄❤️
Thank you so much for the video, it is genius! May I ask if the electric fields of the light waves are always fluctuating in a single plane or they rotate through time? thank you so much
Hi Eduard,. Yes the polarization plane of the electric field can rotate through time (thus, through space). This is called circular polarization. More info here: en.wikipedia.org/wiki/Circular_polarization#:~:text=In%20electrodynamics%2C%20circular%20polarization%20of,the%20direction%20of%20the%20wave.
Very good 🙏🙏🙏🙏🙏
May God bless you Sir.
Really beautifully explained, not even my physics teacher could explain it the way you did, respect mate!
Thank you Driftin! Maybe you can show the videos to your teacher -)
Thank u, it's an interesting video and really helpful
Merci Carolina, I am happy your enjoyed my work!
wow , what an explanation
Thank you Nitesh :-)
very very very good video thank you!!!!
Thank you!
Thank you sir
Thank You So Much Sir 😊
You Helped me a lot
Hi Pratiksha, I am glad o be of help!
Thanks a lot, from a chemist at the university of Dodoma, all the way from Tanzania
Hi Mapato, thank you, greetings to you too, from the other side of the world
(Being a GenX, how far the Internet has gone remains an amazement for me. It is so common in everyday's life nowdays, that we don't realise it anymore... and take it for granted, but if you think about it, it is truely amaxing!)
❤️ thanks a lot ❤️
Well explained thankyou sir 👏 👍 ❤
You are welcome Chenuka :-)
I got first aware with this phenomenon from the experiment of faraday. My head was hurting how such thing was possible. It takes a special kind of talent to explain such a complicated phenomena to people who cant understand it, yet! Thank you!
Thank you for your kind words Dennis. My experience as a teacher has shown me that every students, even the weakest one, can grasp notions that are considered like difficult (for example electric potentials). Society / scholar system is very elitist, too elitist for my taste. So progressively I developed teaching strategies to render these notions accessible to all. And when I have some time, I produce a video presenting a notion for which I developed this pedagogy for my real life students. I am glad it helps you understand a little more the universe we live in!
Great.. thank u.. ❤️
You are welcome Kathir
Thanks!
Thank you so much for your support Denisep!
When EM wave are represented as a sine wave, for example, top peak represents the amplitude, what does the bottom peak represent
Hi Aamir, you should find what you need to an answer that question in my video: "What are waves?". czcams.com/video/LoRRE2aG3AY/video.htmlsi=alXB8FrPioNMT-hb
The amplitude is the difference between the highest position (what you call the top peak - the max y of the sine curve- which is also called a 'crest'), and the equilibrium position (y = 0). For an EM wave, it represents the maximum value of the oscillating electric field strength (check my video, what is an EM Wave)
The bottom peak (called a trough), is also a maximum displacement (in the negative direction this time). For an EM wave, it represents the maximum negative value of the electric field strength. Thus, it also also represents the amplitude.
I Enjoyed video
Very nice channel. New subscriber ❤️
Thanks
Im going to guess that it's going to be something to do with the distance thing you were talking about. Every time you turn the filter the wave lengths change because the filter holes change radius's which limits which light goes through. This was hinted earlier in the video when how color is created in light
Hi Robert, i do not really understand what you are referring too. A polarizer is not a diffraction grating... (it does not disperse light into its frequency components, but only let pass through it a geometrical component of the oscillation of its electric field)
Beautiful way of explaining and making it easy to understand. Thank you sir
Impressive Video! Can show why sound wave cannot be polarised when passing through a polaroid . Thanks
Hi Lawrence. Soundwaves are longitudinal waves: the oscillations of the particles of air are parallel to that of the direction of their propagation. This is why soundwaves cannot be polarised. On the other hand, Light can be polarised because it is a transversal wave (the oscillation is perpendicular to that of the direction of propagation) . I hope this helps!
Thanks for the prompt reply. Can show with a diagram why oscillations of the particles of air that are parallel to that of the direction of their propagation cannot be polarised.
@@lawrencelam2333 I don't have a diagram, but maybe this will help:
Imagine that you could trace a line along all the positions of an oscillating air particle. The particle oscillates from left to right, so that line would be horizontal. And it would be in the same direction as the propagation of the sound (the same direction than the longitudinal wave).
Now place a polarizer in front of it, like in the video. The line you drew would cross the polarizer in one point only… The wave would just pass through unchanged, whatever the direction of the polariser’s axis…
How does the polarisation of light be affected by the arrangement of molecules....explaination in terms of absorbing and emitting light please....thanx
Hi David,
That would be too long to explain in one comment. Rotation of the polarisation plane by molecules is called circular birefringence. I invite you to consult this wikipedia article that is pretty good: en.wikipedia.org/wiki/Optical_rotation
Enjoy!
Thanks sir
thanks saved my lab
thanks
Genius
I am from India, very good explanation
Thank you Chiranjit :-)
Is it the electric field you consider for direction of light ?
that's 10^15 times a second...
Good
🙏🙏🙏 really sir
Prof, Is there any polarizer that can polarize magnetic waves?
Hi Ellios, if you have a magnetic wave (Magnetic Field density oscillating), that means that you also have an electric one that is induced (Maxwell equations). So that results is an EM wave propagating, or light :-). So, to answer your question, any light polariser is also, naturally, a magnetic wave polariser.
@@PhysicsMadeEasy Hi prof and thank you so much, I thought polarizers only polarize the electric part of the EM waves. because they only talk about what will happen to electric wave and I couldn't find a vid that explains what will happen to both waves...because the two waves always
have to be perpendicular to each other in EM wave so I was wondering if... for example a polarizer only allows waves that are oscillating in vertical plane...so the outcome will be magnetic and electric waves that are oscillating in one plane so they are no longer perpendicular?
sorry for writing too much and sorry if my Eng is not good
I like it.
A light wave is a elektromagnetic wave, if at one point light is polarized vertically, then what part of the elektromagnetic component are we talking about? Do we say its vrtically polarized because the magnetic component is oriented that way, and what happend to the elektro component, is that vertically also?
When we are talking about a vertical polarisation axis, the term 'vertical' applies to the electric field: It means that only the vertical components of the electric fields will be allowed to pass through.
The magnetic component of an EM wave emerges from the oscillation of the electric field. The oscillation of that magnetic field is in a plane perpendicular to that of the electric field oscillation. Therefore a vertical polarisation axis will allow the horizontal component of the magnetic field to pass through.
Are you saying that the polarizer is letting the electric component of the wave pass and blocking the magnetic component? Then, the magnetic component emerges after the electric component is past the polarizer? I'm basically trying to understand if the polarizer is temporarily removing one component of the wave as it passes through the polarizer.
@@kn0w0n3 Hi, In regards to the EM Wave itself, saying that the polariser acts directly on the MField, or that the MF is re-induced by the polarised EField is an equivalent statement. I would tend for the second one though based on of my understanding of Maxwell equations
For me, what a polariser does is just cut the component of the electric field strength that is perpendicular to the polarisation axis...
So what about magnetic Field of Electromagnetic ray
Hi Jaya,
Within the scope of classical physics, Light is an oscillating electric field (See video what is an EM Wave). When an electric field oscillates, it automatically generates an oscillating magnetic field perpendicular to its oscillation plane. When you have one, you have the other. So to describe an EM wave, you just need to look at the electric field to describe it, because the magnetic field emerges naturally from it.
The Magnetic components is only affected by a polariser because of how the electric field components are affected by that polariser... Example: if a polariser has a polarisation axis which is vertical, that means that only the vertical component of the oscillating electric field will be allowed to pass. This is equivalent to say that only the horizontal components of the magnetic field will be allowed to pass through.
thank you for using your oven rack and bass guitar cable
Sometimes a teacher needs to get creative :-)
Hey, super smart guy
One question
Is a rainbow polarized light ?
If so is it because the rain falls in one direction🤔
Hi Izzy,
Light in a rainbow comes from the reflection of sunlight inside water drops (the sunlight enters the drop by the front of the drop, refracts, travels to the back of the drop, reflects at the interface between water and air, travels inside the drop again in the other direction and refracts again when it comes out.)
For reflected light to be polarized, the incident light needs to arrive at the reflecting interface at a specific angle, Brewster’s angle. Light will arrive in a small range of angles at the reflecting surface: so some of the light of the rainbow will be polarized, but not all of it (usually 95% is actually polarized).
The direction of the rain (the direction of the velocity of the droplets) has nothing to do with it, but the position of the sun might!
Prof, what is amplitude of unpolarised light?
The amplitude of the light is proportional to the square root of its intensity (Intensity = Power the light provides on a surface per unit surface.)
@@PhysicsMadeEasy I’m asking because let’s say we have unpolarised light to polarised light. As mentioned in your video, intensity of polarised light will be halved - that I understand. But what about the amplitude of unpolarised light to polarised light? Why doesn’t it change? I noted that the polarised light would have I/2 and A. So why A? Is the unpolarised light having amplitude A as well? Or some other value? Thanks for answering
THAK YOU SO MUCHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH
You are welcome Maidagul
Does both the fields exist in polarized light?
You mean both electric and magnetic fields? Yes, always, whatever the character of the light.
@@PhysicsMadeEasy but in most of the videos and online articles only elertric field is talked about in polarized light