Polarisation of Waves – A Level Physics

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Published on January 26, 2015 by

Only transverse waves can be polarised, this video explains why. It also shows why sunglasses are known as 'polaroids' and how you can test this yourself on a sunny day.

Update - Please note that the reflected light waves from water are actually horizontally polarised:

https://www.osapublishing.org/DirectPDFAccess/70EF21F6-C0C6-DC00-994222A32CB6DCEF_276371/oe-21-26-32549.pdf?da=1&id=276371&seq=0&mobile=no

Thanks for watching,

Lewis

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68 Comments

  • adnan solanki 7 years ago

    great video but please make it a bit darker. Its too bright and it hurts my eyes, maybe put a polarized filter on the camera, ;P

    • William Preston 6 years ago

      Haha probably, I am not sure if the original comment had the pun on the end of it when I replied though. Either way, I might’ve been sarcastic at the time as well, I can’t remember since it was over a year ago :’)

    • Sh Al 4 years ago

      why would you reply after a year

    • Raquel Florence 4 years ago

      Sh Al Just like you replied to a comment made 2 years ago

    • imr 3 years ago

      @Sh Al r u clapped

    • Captain Aviator 3 years ago

      @imr shut up

  • Momen Ibrahim 7 years ago

    That was so cool! Thank you for this!

  • JI ji 7 years ago

    THANKS FOR HELPING ME….

  • HAMDANI YUSUF 6 years ago

    4:29 the polarized reflected light should be drawn as dots, since the direction of the field oscillation is in & out of the drawing plane.

    • tenochtitilian 6 years ago

      +HAMDANI YUSUF (dani)
      Good observation thanks for that.

  • HAMDANI YUSUF 6 years ago

    At Brewster’s angle, the reflected and refracted rays are mutually perpendicular

  • crog ting 6 years ago

    Best physics channel on YouTube, can’t thank you enough

    • A Level Physics Online - Year 13 6 years ago

      +crog ting Thanks – can I quote that on my website?

    • crog ting 6 years ago

      +A Level Physics Online – Year 13 yeah mate go for it

    • A Level Physics Online - Year 13 6 years ago

      Thanks. Good luck in your exams.

  • Ieuan Gundy 6 years ago

    This guy needs more subs

    • Ieuan Gundy 6 years ago

      Your channel has helped me SO much. Fast, to the point, EASY explanations. KEEP UP THE GREAT WORK!

  • Rabin Kandel 6 years ago

    I think that light reflected from the water surface is plane polarised in horizontal plane(not in the plane as you drew) .
    When you use sunglasses it only allows light in vertical plane blocking glare ( that is horizontally polarised when reflected. Typical question of this type appeared in June 2011 G482.

    • Physics Online 6 years ago

      You’re right. Thanks.

  • Zakariya Abdullahi 6 years ago

    After a year of looking for a good physics Youtube channel, finally found it.

  • Tom Stalley 5 years ago

    nice shades bro

  • Nurnabi Haider 5 years ago

    i think for the first time i could see his face

  • Google User 5 years ago

    How come when you put sellotape over the filter, light can pass through it even when the second filter is perpendicular? Whats the reason to this?

    • TheGeekSoup 4 years ago

      Molki Bolki I think it’s because light still reflects off of the object in between the filters so it will have light with an electric vector in all directions hence thee electric field that’s perpendicular would pass through the second filter

    • Thatgeezer 1 3 years ago

      Think it’s because the sellotape acts as a third polariser.
      So the first polariser only allows the vertical component of the lights oscillations to pass through. Polariser 3 (the sellotape) would only let a component of the vertically polarised light through as its axis of transmission is not perpendicular to that of polariser 1.
      Then the plane of oscillations of the light reaching polariser 2 is not perpendicular to the axis of transmission of polariser 2 and so a component of this light will pass through.

  • khatira sharifee 5 years ago

    can’t thank you enough

  • SBTC Trọng Khangg 5 years ago

    Keep going guy, you are great!!

  • Sohan Roy 5 years ago

    awesome! explanation

  • ZAVELLI 1800 5 years ago

    what do you mean by the analyzer? , is it just the second polarising filter

    • Physics Online 5 years ago

      ZAVELLI 1800 yep, that’s all it is.

    • ZAVELLI 1800 5 years ago

      do you get questioned on malus’s law. What type of questions would they be ? are they calculation wuestions

    • Physics Online 5 years ago

      ZAVELLI 1800 You would for OCR spec A, but not for AQA.

  • Tashfeen Ahmed 5 years ago

    Can someone please tell me a simple definition of polarisation ?

  • ahamed akmal 5 years ago

    please explain this statement ‘oscillation of polarized is in a single plane which includes direction of energy transfer but direction of oscillation is perpendicular to direction of energy transfer ‘

    • FireWarrior2013 5 years ago

      ahamed akmal It means that the “motion” of the wave is is directly right angles to the motion of energy (which is just a straight line basically.)

    • ahamed akmal 5 years ago

      yes i get that part , but ‘oscillation is in a single plane which includes direction of energy transfer’ what does this mean

    • FireWarrior2013 5 years ago

      @ahamed akmal you could easily draw it on a piece of paper as though it was two dimensional. Basically, all of these are travelling on a singular plane, no matter which wave passes through the polariser.

  • UDAY KUMAR 5 years ago

    only 270 likes this video deserves more….

  • swalstar 5 years ago

    Please can you explain the selotape bit at the end?

  • Turjo💀 4 years ago

    loved it!!! awesome 👌👌👏

  • I like Airplanes ok 4 years ago

    5:26 how does it work, edexcel asks

  • Layan Jabr 4 years ago

    Stupid question but why can’t longitudinal waves be polarised ?

    • Sea 3 years ago

      some person they are already plane limited to the direction of energy travel (parallel)

    • Taiwo Thomas 2 years ago

      @Sea so they always move horizontally?

  • Chris Wesley 4 years ago

    Another nice video, thanks. At 4:37 you combine two phenomena by saying the reflected light is polarised and creates a glare. But I don’t understand what one has to do with the other – since polarisation REMOVES light from a source, why should the polarised light cause more glare than otherwise would be the case?

  • xtdycxtfuv 4 years ago

    Hmm that’s really fascinating. Thank you for this.

  • Nilo Sa 4 years ago

    I think the reflected light is partly polarized not plane polarized ?in 4:30

  • Giles Wood 4 years ago

    According to the video, a polariser that is vertically orientated it only lets through the vertically polarised light. So are we saying that is doesn’t let through the light that is at 5 degrees off the vertical? 0.0001 degrees off? If this was true then only a tiny fraction, perhaps an infinitesimally small fraction, of the light would be let through. So what part is actually let through? Common sense suggests that light up to 45 degrees either side of the polariser’s angle would be let through.

  • tom111 4 years ago

    reply to this comment in 2022. first reply gets a reward.

  • UAwulf 4 years ago

    Glad i got to know about tjis channel even though i’ve only got one month for my AL’s here in Sri Lanka!!!! Thank You Sir!!! Your awesome!!

  • Noem Í 4 years ago

    the card models were really helpful

  • Yamini C 3 years ago

    language isdifficult to understand

  • asif alam joy 3 years ago

    What is the meaning of plane polarisation?

    • Sea 3 years ago

      asif alam joy allowing the light to only oscillatie in one direction

  • HOIX THE GREAT 3 years ago

    Malus’ law isn’t required on AQA (It is on OCR), so no point learning it if you’re an AQA lad

  • Dhwani Selvam 3 years ago

    Its hard to study this but made it easy with illustration

  • Ajay Reddy 3 years ago

    i have a doubt which i googled, but even didn’t get any answer. my doubt is, ” when light passes through a polaroid, electric field components of light in one direction is absorbed . what happens to the corresponding magntic field ?, as light is combination of electric and magnetic field. i mean will the magnetic component in one direction also get absorbed or not?”. Can you please clear my doubt?

  • Sciety 3 years ago

    Nice way of teaching. Now only i understand this

  • Sea 3 years ago

    Thankyou!

  • Gyanjit Mahapatra 2 years ago

    cool

  • keshav birari 2 years ago

    From where u get Polaroid

  • Faceless 2 years ago

    People DO NOT think that the EM waves goes through the gaps in polarising filters… Unless you are told that “the exam board thinks this is right so think this” but really this is not true. The aerials in a polarising filter absorb the waves oscillating parallel to it. They work just like a radio aerial because when the aerial is down nothing is absorbed because the radio waves have no horizontal component only a vertical one (they are polarised) but when it’s up it absorbs the wave. Now if you believe the gap idea… where are the gaps in the radio aerial and why would a light polariser work any different.. light is also an EM wave (BTW light is not the only thing that can be polarised, as far as I’m aware any transverse wave can be though I really wouldn’t know how unless it’s an EM wave because it’s the electrical field and magnetic field of the aerials that absorb just one orientation…) sooooo the wave will only be absorbed by the aerials if they are parallel to the electrical component of the wave.

    P.S. If I mention the magnetic wave that’s more just me applying my honestly limited knowledge because the electrical field has a much greater magnitude so it’s the only one I ever hear about but IK the magnetic field is perpendicular to electrical field in both EM waves and in Flemming’s hand rules.

    If anything I said was explained poorly just ask.

    • Physics Online 2 years ago

      You are right, I made a video about the truth here:

  • Benjamin Sumner 2 years ago

    Why wouldn’t you explain that a vertical filter allows the vertical component of ALL the angles of polarisation to go through and similarly the horizontal filter, the horizontal components? You describe it as if every angle of field except the light in plane with the polariser are just absorbed so students will expect a tiny fraction to go through a single filter. In fact 50% goes through

  • tri mukherjee 2 years ago

    thanks so much for this video 😀 i’m doing classes from home (corona) and it’s really clear and useful

  • Nitesh Kanwar 2 years ago

    Thank u soo much. Very helpful🙏😊👌

  • KingLegend76 2 years ago

    1:55
    How does that block it all????? There is still a tiny line that made it through

  • Shivansh Gupta 2 years ago

    Never seen such diagram in 2d
    AWESOME

Comments are closed.