The Photon – A Level Physics

Published on February 23, 2015 by

What exactly is a photon? this video shows how we can use the particle model, with individual corpuscles of energy, to explain certain properties of EM radiation.

If you want to find out more about the photon then I can highly recommend you listen to this radio show:

Thanks for watching,



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  • Mohammad Ali 7 years ago

    +A Level Physics Online doesn’t the mass of an object increases as it approaches the speed of light. so the photon’s have mass?

    • Physics Online 7 years ago

      @Mohammad Ali You’re correct that when an object approaches the speed of light its mass does increase, but that is only for objects that have a mass to begin with. For example, an electron has a rest mass of 9.11 x 10^-31kg, but when its speed approaches c it will get heavier, in fact it can never get to the speed of light because as you give it more energy this only increases its mass not its velocity. But photons start off with zero mass – some objects have mass, some don’t. Some are charged, some aren’t etc.

    • Mohammad Ali 7 years ago

      @A Level Physics Online Thanks, that really clears things.

    • Mohammad Ali 7 years ago

      @A Level Physics Online Do u have the ocr 2014 past papers?

  • Phil Gowans 7 years ago

    Great vid. Nice pen too!

  • Legion Liberator 7 years ago

    pretty awesome video! this explains a lot!

  • Edward Lucas 7 years ago

    That constellation..was that Orion ??

    • Physics Online 7 years ago

      +Edward Lucas Well spotted, I even tried to match the Lego to the intensities of the real stars. I once spent many months sleeping outside in the desert and that was the one constellation that I saw every night and could recognise!

  • Izzy Manuel 7 years ago

    I was wandering if you have any videos on Quarks and Leptons, and Matter and Radiation?

    • Physics Online 7 years ago

      +Izzy Manuel Not yet but I will do – in the next few weeks hopefully.

    • A Level Physics Online - Year 13 6 years ago

      +Izzy Manuel These videos are available now.

  • peter gahlert 7 years ago

    Photon= Light !” The secret of light ” by Dr. Walter Russell…Quote :” In the wave lies the secret of creation ” Thanks

  • Fabian Kempinska-Larsen 6 years ago

    Ur fat

  • jakeflow 6 years ago

    What exactly is a photon? A word made up for persons that don’t understand what light is

    • Physics Online 6 years ago

      +jakeflow27 If you understand light truly then you realise it isn’t exactly a wave and it isn’t exactly a particle. It is both and neither, light can only really be expressed mathematically but we use models in science to explain (and understand) the behaviour of the world around us. Think of light travelling like a wave and interacting like a particle and that will help.

  • Rizwana Akmal Khan 6 years ago

    please make a video explaining “Band Theory”’s newly added in the syllabus for 2016. MUCH appreciated, thanks!

  • Isatou Bah 6 years ago

    you have such amazing videos. i tried looking at some of your year 13 videos but it says its not available your country.can’t you do something about that

    • Physics Online 6 years ago

      +Isatou Bah I’m looking into a way to have another website with the Year 13 videos available for those who can’t access the YouTube paid channels due to the country where they live. But it won’t be for a while I’m afraid. Any ideas or suggestions of other sites that have something similar?

    • Sai Sriramagiri 6 years ago

      +A Level Physics Online Vimeo? Daily Motion?

  • Amin Shadowz 6 years ago

    What exactly is the difference between photons and quanta?

    • MediaWMLV 5 years ago

      Quanta is the plural form of quantum. A quantum being the smallest ‘component’ of anything. In other words, you cannot have half a photon, the photon is the smallest component of light (or electromagnetic radiation to be more precise). So to answer your question; a photon is the quantum of light, but you could also say that photons (plural) are the quanta of light.

    • CJ 4 years ago

      Quanta is an airline out of Australia. Also, the airline has very small planes.
      And photons is the gangsta way to say 4 tons.
      For example, the gansta way to say ‘fifty’ is ‘fiddy’.

      Got it?

    • shady shane 3 years ago

      @CJ yeah, i ain’t got no tree fiddy, “And photons is the gangsta way to say 4 tons.”, that’s inspired.

  • Elias Barnard 6 years ago

    Nice pen

    • Just Imagine 4 years ago

      Indeed, nice pen!

  • Mark Hardy 6 years ago

    Your videos are always helpful. I appreciate your use of props in your videos. I can’t learn well without them.

  • Arun Singh 6 years ago

    u have got an inborn talent of explaining well

  • abc def 6 years ago

    despite of a popular belief, i have no idea how planck’s got his h. Einstein method is crystal cear to me E – Eo = h f, an electron escapes with the energy h f, the simple slope is THE h, therefore a photon itself is quantized.

     but in planck method… i really have no idea… the impression i got from Einstein’s words on planck was like, planck method was wrong, his derivation was wrong. just only his result was correct… i even tried to understand the vibrational modes of the molecules of the walls of the cavity in black body.

    if i use the bose-einstein statistics then i may be… but it is hard to see where the quntization is started.

    I dont care about the result, i like to know how he got it and got it quantized

  • niebieskieucho 6 years ago

    Picture of the single photon is already known

  • Limitless 1 6 years ago

    great video

  • usef bmf 6 years ago

    So some of the stars we see now are already dead , the more distance the older it is wow , it’s actually amazing it u think of it

    • Physics Online 6 years ago

      We’re not seeing the Universe now, everything we see is in the past – it also takes your brain a short amount of time to process the visual signals!

    • usef bmf 6 years ago


  • A L 6 years ago

    thankyou! that was very neat . i was really confused about how the atomic spectrum worked this cleared things up!

  • Carly Bailey 6 years ago

    you taught me more in 4 minutes than my teacher can in 2 hours… 😂

    • Physics Online 6 years ago

      I’m sure your teacher is doing a good job – it’s not easy! But thanks for your comment, really appreciated.

    • Joe AF 5 years ago

      Kristian Mooney According to my GCSE teacher they will still travel at the same speed but they travel a longer distance because they bounce off other particles. Therefore making the time longer but the speed constant.

  • Fareeq Abel Hammed 6 years ago

    why is ur videos free ? thanks a lot i thought a2 part is paid

    • Physics Online 6 years ago

      I made everything for AS Physics free, but I did make the decision to charge a small amount for the Year 13 videos to allow me to keep making videos. I’ve made them all completely on my own and they do take a lot of time (and money) to create.

    • Fareeq Abel Hammed 6 years ago

      @A Level Physics Online kindly make video on “band theory”

  • Valkriecain99 6 years ago

    The graph at 1:20….must be wrong right?

    • Darren Animatic 3 years ago

      I don’t think so.

  • Mario Brega 6 years ago

    Great video!

  • Thomas Drowry 6 years ago

    Photons don’t travel for millions of years across the universe, they travel instantly in their own time reference.

    • Your Waifu Sucks 5 years ago

      Thomas Drowry Yes but only in their own frame of reference.

  • Hfanstar 6 years ago

    ever thought about making a patreon page or similar for donations, means those that want see more can and those that cant afford it are still able to access it, just and idea, great videos though.

  • Alpha Centurai 6 years ago

    Dude, what?

  • Shitpostin' Productions 6 years ago

    Your video was awesome, and every helpful, though you said that being that a photon has a mass of 0 it can ONLY travel at the speed of light. I have seen a video where a group of scientists slowed down light, so how is that posible?

    • Matt Whitelock 5 years ago

      I believe when he says that, there is an implicit “in a vacuum” – something with a mass of 0 can only travel at the speed of light in a vacuum (eg in space). Light slows down ever so slightly when travelling through air, and quite a lot when travelling through water or glass or other similar materials, causing refraction and other phenomena.

  • under taker 6 years ago

    Sir I am ur fan plz autograph

  • purple muffin 5 years ago

    Hello sir, I would love to subscribe and pay for your year 13 channel, however it’s not available in my country, so i wanted to ask whether this playlist is enough to make me understand the chapter quantum physics from the A2 syllabus ? Thank you. 🙂

    • Physics Online 5 years ago

      basmah It should be. The paid channel is just for the year 13 content.

  • SPAAAAACE 5 years ago

    I misunderstand; if gamma particles have mass, then they’re definitely not photons, so why did you say they were?

    • Unl345h3d_5t4r 3 years ago


  • Fatima Hayssam 5 years ago

    Does it mean that photons act as waves ??? Is H constant plunck means the lowerest energy of a photon ?? thank you

  • santiago santana 5 years ago

    so if the star is dead ¿when will we stop reciving its lights?

  • santiago santana 5 years ago

    what the meaning of more or less energy its means that the particles are bigger and smaller or it means that happen more or less often? besides how its posible that soething that has energy doesnt has mass doesnt suppose to be the kind it the same (mass/energy)?

  • Arun Ramula 5 years ago

    Sir simply what is difference between photon and electron….!!!! Pls pls tell sir sir pls pls

  • Avery Molinsky 5 years ago

    hello I was wondering whether light had memory like a record can be imprinted with sound, if light is imprinted in a like manner after all it is not the object you are seeing but the light reflecting off of that object that you actually see. and if that imprint would be permeate, or would it be able to record in a layering effect retaining each reflection as it travels on it’s journey. or is it just rewritten each reflection. also since light is made up of all light spectrums and the thought is that photons have a chemical reaction going on weather the colors we actually see are in fact that color or is it a combination of two colors producing a third color being the color we see. two chemical reactions producing the color change effect. also if this is not the proper forum for this discussion could you or anyone direct me to an appropriate forum.

  • Ambience 5 years ago

    Why does the textbook say electrons in an atom only ‘absorb’ photons of a particular wavelength. Can’t it not just absorb every single photon with a greater energy above the principle one? I noticed the black-body curve looks like the curve for resonance for intensity against frequency. Are these too linked? It will still absorb photons above the principle but not as much as the resonant frequency photon?

    • Physics Online 5 years ago

      An ambience for every occasion It has to be exactly the right amount.

  • tom eagle 5 years ago

    Look for the new difinition of the colorfulness of photon on SALEH THEORY group’s youtube chanel: Saleh Theory-com

  • Stephen 5 years ago

    Why does the diagram at 1:15 show a bell curve? Does that mean green is the most energetic color of light?

    • Slow Satsuma 4 years ago

      Stephen Ball It means that bodies don’t emit much high energy radiation because they don’t have enough energy to do so. Most bodies emit most of their radiation infrared radiation.

  • Astatonic 5 years ago


    • Physics Online 5 years ago

      Astatonic good luck

    • Astatonic 5 years ago

      thank you and paper went well 😀

  • john michael 5 years ago

    you said photons…how???
    A photon is precision engineering at its finest…what factory is out there that can produce so many identical photon???
    The answer is no factory. You may want to rethink

  • Ray Kasprowicz 5 years ago

    Question – regarding EMF, which energy source produces the photon, electricity or magnetism?

  • ChaosCal 5 years ago

    I am amazed that a photon travelled millions of years just to reach me, I feel blessed

  • Ava 5 years ago

    I have a question.
    If you fire a single photon onto a piece of plastic in space, would different observers at different locations be able to see it’s impact?
    If so, does the photon split up in billions of different photons, some of which are received by the eyes of the observers?

  • OHM-968692 5 years ago

    So white light is a combination of a stream of RGB photons or they combine to form one thing? I find this wave/particle property of light still difficult to understand.

  • Jeff Donhauser 5 years ago

    thank you

  • Random Kritz 5 years ago

    Radio waves are longgg bois

  • Random Kritz 5 years ago

    “Einstein’s Mistake?”

    In 1917, when Albert Einstein (1879 -1995) set out to describe the Universe mathematically, he included a “cosmological constant” – an outward force to prevent the Universe from collapsing. At the time he did not know that the cosmos is in fact expanding. His “mistaken” idea has recently been recieved with the concept of dark energy.

  • Gen3Benz 5 years ago

    Those aren’t photons! Those are Legos!

  • Entradinha Bonita 5 years ago

    I still don’t get it!! If the photons does note make up the wave, and the wave is not “inside” of the photon, otherwise we would have city sized photons, whats is the wave then?? What’s wavering??

  • nmarkose 5 years ago

    Great video man. Thank you

  • martin soldén 5 years ago

    A photon is any pack of energy With A charge of O.  Spin of 1 With two possible orientations and a rest mass of 0…Pretty simple really

  • Life is Wonderful 5 years ago

    Using LEGO bricks? Brilliant! Very good quality video!!

  • Phil Dobson 5 years ago

    The truth is a photon is just a mathematical particle because Einstein’s principal skill was imagination. Electromagnetic energy is oscillations in magnetic field. The smallest oscillation is *one wave* The amplitude of ‘waves’ can also be increased, which is how AM radio works, (Amplitude Modulation) Below 2 MHz radio waves are diffracted (bent) by the magnetic field of the Earth. (Converting into mathematical particle photons is really unnecessary = time consuming.) But plenty of professors have gotten plenty of time 2pac out!
    Light is electromagnetic oscillations at 430 trillion hertz – 770 THz (not three different coloured little balls)
    Example:If you have a 1watt transmitter you could divide Watts by 3600 to make it Watts per second to do the Maths with Hz (oscillations per second) of your transmitter whether it was single frequency LED light or a radio frequency used by your Smartphone phone, to find out what energy in watts your mystical mathematical particle has!
    But hay, manufacturers can make Smartphones, using quantum mechanics, with several different electromagnetic transmitters from Bluetooth to Wi-Fi to HD screen, without using photons in the calculations!

  • Letty Yeah 5 years ago

    Hi bit confused are EM waves made up of photons or just photons are how they deliver energy

  • v Bremont 4 years ago

    Images could be the vehicle of the quantum photons medium to understand us. As energy is created, vision creates frequency, and a pocket of information is displayed on the watercolor.

  • Red Shift 4 years ago

    Photons do actually have mass; it’s just that the mass of a single photon is so small, its almost unmeasurable.

    • Mairis Bērziņš 3 years ago

      If that would be the case then they wouldn’t be traveling at the speed of light.
      Even if you think about photons as electromagnetic waves. All you have is 2 fields having oscillations in them simultaneously. It’s like saying water in a wave weighs more than the water thats not in a wave.

  • ibraheem saleem 4 years ago

    Since they all travel at the speed of light, what do we mean by a more energetic photon?

    • Mike 3 years ago

      has a higher frequency

  • Desmond Hume 4 years ago

    So the photon is the epigenetic result of consciousness itscellf

  • Just Imagine 4 years ago

    Lost at second :29.  Geez.   Stop, stop!  How can light be affected by gravity if mass is truly 0?  Shouldn’t all of this have the caveat… “according to current understanding?”

  • HollyBlossom 4 years ago


  • Ali Raza 4 years ago

    You are great sir
    Please speak slow

  • Darren Animatic 3 years ago

    Quanta of light : photon

  • Muhammad Mirsab 3 years ago

    4:12 CRAZY, and cool!

  • Stomiac 3 years ago

    You lost me at Neuton

  • Captain Yata 3 years ago

    Ah yes, ‘Quautum’ physics

  • Kakashi 2 years ago

    is all of this OCR?

  • helo void 2 years ago

    Is there a date of when it all started the 00:00:00 January 1 ?

Comments are closed.