Diffraction Gratings – A Level Physics

Published on February 2, 2015 by

If you shine light, or other types of EM radiation, through a series of small slits the waves interfere causing constructive interference at certain points. We can then use this method to calculate the wavelength of the light. It is also why DVDs and CDs make beautiful rainbows.

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  • y n 7 years ago

    This is honestly a really great set of videos, thank you very much.

  • Izmritzs 7 years ago

    Keep these videos coming. These are really helpful!!

  • Choiᄒᄋ커플 7 years ago

    thank you so much^^

  • Jorgey Boy 7 years ago

    very clearly explained, thanks

  • Shatha Barq 7 years ago

    Thank you!

  • Oshy Chan 7 years ago

    well done , very clear explanation , helped me a lot

  • Arromal J Jayan 7 years ago

    Hello Mr Matheson
    Really amazing videos!! Just wanted to know if you would be going through A2 also….because literally, your videos very helpful to us students….we have full support for you sir!!

    • Physics Online 7 years ago

      @Arromal J Jayan Yes I will, still finishing off AS but A2 will be next!

  • Suma Al Bayatee 7 years ago


  • Moinul 7 years ago

    What board are these videos mainly focused on?

    • Physics Online 7 years ago

      @Moinul Islam Mainly OCR Spec A, but there is some content for some of the Edexcel and AQA units (I’m still working on the rest of this content), although physics is still physics whichever board you’re sitting which is why I haven’t mentioned any exam boards in particular in my videos.

    • Samaa سماء 7 years ago

      @A Level Physics Online I’m taking IGCSE and it helped me a lot! Thank you so much!

  • 83Visual 7 years ago

    exam tommorow here I am again last day revision, anyone on the same boat?

    • Tom Stalley 6 years ago

      how did it go?

    • Fabian Johansson 5 years ago

      I’m here the morning of my presentation at school, I am so screwed.

    • hans tonra 4 years ago

      lol same

  • Kimberly Ann 7 years ago

    Thanks so much, very informative!

  • Shella 7 years ago

    Brilliant, simple and concise! No bullshit. Saves time. Great vid

  • viralshield 7 years ago

    oh, ok 🙂

  • FattyWayne 7 years ago

    i learn more in 6minutes than in a lecture at school

    • Skatty kid 1 2 years ago

      Well done mate u want us to suck u off

    • Coolfred 2 years ago

      @Skatty kid 1 What’s your problem?

    • Dench773 2 years ago

      @Skatty kid 1 wtf xD

  • Jeyaneepan Kanagaratnam 7 years ago

    consider a one-dimensional array of scatterers with spacing s=1.5 microns. I shine a light of 532 nm wavelength perpendicularly onto this array and look at the back-scattered light on a screen far from the array.

    How many diffraction “spots” should I see on the screen? Please enter an integer number.

    • Waddia S. 6 years ago

      d = 1.5 x 10^-6 m
      lambda = 532 x 10^-9 m
      For maximum n of fringes/ spots,
      theta = 90
      therefore n = (d.sintheta)/ lamba
      You’re gonna observe 2.8×2 = approx 6 diffraction spots
      Correct me if my discretion is wrong. And thanks for the food for thought 🙂

    • Jeyaneepan Kanagaratnam 6 years ago


  • Kriti Gupta 7 years ago

    my all doubts are cleared by watching this….thanks

  • Physics Online 7 years ago

    Want to see more videos I’ve made? Have a look at this video: What else should I make videos on next?

    • Physics Online 6 years ago

      Vinay Khandelwal I have a complete playlist for SHM. Have a look on my website for the list of all videos.

    • s s 6 years ago

      @A Level Physics Online Right. Thanks!

    • Tejinder 6 years ago

      you should make videos on Material Physics

    • Tejinder 6 years ago

      A Level Physics Online Please make video on Hall effect

    • Fahimus Alimus 4 years ago

      Baryons and Mesons.

  • Panzermeister36 7 years ago

    Your video is really really helpful man! Thank you for your time

  • DJ Spades Productions 7 years ago

    you’re a very good teacher, keep doing what you’re doing

    • A Level Physics Online - Year 13 6 years ago

      +TKDS Thanks

  • Dragana Bogdanovic 6 years ago

    Hello Mr Matheson,
    Amazing videos and very helpful!
    I wanted to ask where we can find 2015 past papers? (ocr board)
    Thank you very much 🙂

    • Physics Online 6 years ago

      +Dragana Bogdanovic They’re not available yet on their main website – but your teachers will have access to them.

  • BUDEE 6 years ago

    Light consisting of two separate wavelengths, 450 nm and 650 nm, falls onto a diffraction grating. The grating is labelled 600 lines per mm.

    Calculate the angular separation between the first order maximum of the two wavelengths.
    Help please

    • Physics Online 6 years ago

      +JBC Jackson Use the equation to find the angle theta for n=1 for each wavelength individually. You answer will then be the difference between these two values.

    • BUDEE 6 years ago

      @A Level Physics Online Thank you!

  • Mo Leily 6 years ago

    Thank you so much your video is very useful

  • MoMax 6 years ago

    hahaha ikr frozon was acctually crap

  • Nafees 6 years ago

    Would the path difference for the first order be lambda or 2lambda??

    • Physics Online 6 years ago

      It would be lambda.

    • САLIMBO ГГГ 4 years ago

      The second order is 2lambda.

  • Dream Ville 6 years ago


  • 198Immortal 6 years ago

    this is the first video i watched from your channel. I love your voice 🙂 and you got a subscriber!

    • AmbieWolfie 5 years ago

      If you take Chemistry, E Rintoul has a similar voice and is brilliant at explaining chemistry concepts 🙂

    • Maisam Askari 4 years ago

      Rintoul is the absolute best

  • Z Kodo 6 years ago

    Great vid keep it up

  • Tejinder 6 years ago

    do you had a video on Solid state physics

  • Simar Singh 5 years ago


  • Ahmad Hassan Khan 5 years ago

    What is d?? The distance between 1st order and O order for example??

    • Sea 3 years ago

      Ahmad Hassan Khan distance between slits

  • Henry Tobiloba 5 years ago

    What happens when a grating of 600lines/mm is used in place of a 300 line/mm grating??

  • Ethan 5 years ago

    wow this is such a good video, so well explained, makes it seem easy. very good job

  • Jordan Randal 5 years ago

    Where can I get a 300 lines/mm diffraction grating exactly like the one you used at 44 seconds into your video? My diffraction grating has 1000 lines/mm and it does not produce higher order image pairs like the one you used in your video. It would mean a lot to me to get the 300 lines/mm grating you used and show my Dad that is does indeed produce higher order image pairs as shown in your video.

    • Physics Online 5 years ago

      Pls AJ I just found this one in a cupboard at school. Could you borrow one from your teacher, and a small red laser, to use at home?

    • Jordan Randal 5 years ago

      I’m in the fifth grade at my school. We haven’t talked about lasers or diffraction gratings yet. It’s my Dad that bugs me about this stuff. At home we got some diffraction gratings that have 1000 lines/mm and a red laser pointer but it doesn’t work. We only get 3 dots no matter what we try. We don’t get higher order image pairs like you do in your video. So we are getting more diffraction gratings with less lines per mm. Yours has 300 lines/mm. In a few days we will be able to try this with 100, 300, and 600 lines/mm. It will mean a lot to my Dad to see the higher order image pairs in his lifetime.

  • Abdelrahman Sherif 5 years ago

    You are a legend!!! Thank you!!

  • fatma faisal 5 years ago

    could u do like an actual question on this? i didnt really get the part where u said we can find theta .. like is it the sin = opposite by hypotenuse way..?

  • Maisam Askari 5 years ago

    Spot on

  • Frobe Kobe 5 years ago

    Wow these videos are great was wondering if you have made one for A2 contents

    • Physics Online 5 years ago

      Frobe Kobe Yes I have, almost the whole course. Have a look on my website.

    • Frobe Kobe 5 years ago

      can I have a link please

    • Frobe Kobe 5 years ago

      This also covers everything on OCR B( Advancing physics) too right?

    • Physics Online 5 years ago
  • Naman Sharma 4 years ago

    Hey i think that the formula is 2d sinθ=n× lanbda and i have a doubt that we can take any value of n. For example- we have 3 dispersed laser pt so we can put value of n= 1 or 2 or 3. Pls reply

    • Chris McMillan 4 years ago

      that’s for a single slit dispersion I think

  • САLIMBO ГГГ 4 years ago

    Does the maximum number of orders include the 0th as 1 of them? Or not at all?

  • Alethea Barretto 4 years ago

    this channel literally the only thing getting me through physics

    • Daniel Clarity 3 years ago

      Woah cool profile picture. Who is she and what is she from?

  • SOLAR 4 years ago


  • boxcat 4 years ago

    Why exactly is theta different for different wavelenghts?

    • Twilight Sparkle 4 years ago

      maybe because different wavelengths have different angles

    • Ediz Ucar 3 years ago

      the amount of diffraction depends on how close the width of the slit is to the wavelength, so light of different wavelengths different amounts for a give slit width, resulting in different values for theta

  • Akbar Adilah 4 years ago

    Thanks bro👊

  • endover 4 years ago

    A question: how would you find/determine the center of let’s say 1st order maximum? Is literally the geometrical center of the fringe, or the place where there is a green color?

    • Twilight Sparkle 4 years ago

      find the tree for the centre

  • Sohaib Baig 4 years ago

    Even though your videos are amazing, the intro makes my ears bleed

  • Yff Svhf 4 years ago

    Thank you

  • Nafia Farzana 4 years ago

    That really helped me. Thanks a lot

  • Sheheryaar Malik 4 years ago

    Which pen do you use?

  • Stan Peter 4 years ago

    Thank you for saving me. You are one of the channels like Khan Academy and Science Shorts that don’t put me to sleep! Thanks a lot for your resources!

    • Physics Online 4 years ago

      Thank you, I try and make it as interesting as possible!

    • Stan Peter 4 years ago

      Yup, your videos are 11/10 😉

  • GlobalLizard925 4 years ago

    Very helpful video

  • Vegeek 1 4 years ago

    Using to support my A level lessons thanks. The students learn more in 6min than….

    • Physics Online 4 years ago

      That’s great to hear! I made these for just that reason, to help students alongside their usual lessons.

  • Don'tMeanToBragBut 4 years ago

    so does theata change depending on the order your measuring from or is theata always the angle between the zero’th and first order???????

    • Ediz Ucar 3 years ago

      its between 0th and any order… the ‘n’ in the equation handles that.

  • Muhammad Hamza 3 years ago

    Wow you explain really good !

  • Rebecca Tan 3 years ago

    Single-slit experiment vid?

  • tanjim mahin 3 years ago

    best video for learning……………………………

  • Tanishkaa Deshmukh 3 years ago

    “horrendous DVD Frozen” lol

  • Zoha 123 3 years ago

    Very well explained.This helped me a lot☺

  • consciousnick - 3 years ago

    Whoa, sweet interference pattern.

  • Ketch Urself 3 years ago

    Im wataching you because my teachers can’t explain things. Started as level physics this september and i want to get A* at a level.

  • hamna chaudhary 3 years ago

    This lecture was sooo amazing. You taught us practically.

  • T B 3 years ago

    Is this the same video upload on Up-learn?

    • Physics Online 3 years ago

      Yes it is, they use my material and have plenty of other questions too.

  • Colamity 3 years ago

    Hey, listen buddy. I like FROZEN, so don’t you dare call it a horrendous dvd.

  • Jordan White 2 years ago

    @physicsonline do AQA students need to know how to convert degrees into DMS for this topic?

  • incredible man 2 years ago

    i hate frozen but nice video

  • Nahula Luckshman 2 years ago

    thank you

  • KrazylassPlayz 2 years ago

    As someone who has as of yet never done a proper lesson of A-level physics trying to understand some of the course before I start doing it in September, this was very well explained. Thanks very much.

    • Physics Online 2 years ago

      Glad it was helpful!

  • Mutasem Wahbeh 2 years ago

    It was the best explanation thank you !

    • Physics Online 2 years ago

      You are welcome!

  • Edith Corkery Schless 2 years ago

    is this a practical video or just an excuse to hate on Frozen? Experts still don’t know

  • Vikturr 2 years ago

    god bless you

Comments are closed.