Diffraction, Interference & Polarisation: GCSE revision

[@wasymuzaffar4531]

Nooooo I only found you 3 hours before my exam.

[@engdallal]

Thank you very much Dr. Physics I hope you introduce yourself to your subscribers soon. I wish to know you

[@CraftyF0X]

Another excellent video sir ! Just one question, so if the polarisation filters out the "other directions" from the light, where do they go, are they absorbed or reflected back by the filter ?

[@LorenzoPetralia]

the polarizer will absorb impinging light of one plane of polarization. ----- en.wikipedia.org/wiki/Polaroid_(polarizer) ----

[@DrPhysicsA]

Could be either but I have done a series of videos on electromagnetic waves (degree level) [in the E&M playlist] which shows under what criteria EM waves are reflected or absorbed.

[@apoorvaaps4066]

Hello Sir, I am a great fan of your videos.Have a doubt though. At 8.09 you drew a graphical representation of the interference pattern obtained by Young's double slit experiment which shows a decrease in the intensity of the bright fringes from the center. But I think that the fringes obtained as result would be equally spaced with the same intensities.

[@bradsta114]

Would you be able to sort the a level videos into separate AS and A2 playlists please

[@DrPhysicsA]

The difficulty is that I am trying to cover AS and A2 levels for several different syllabuses. But I have tried to put the videos in a logical order in the playlist and I leave it to students to decide what material they have actually covered in their course and to view the appropriate videos.

[@RealationGames]

Very good video. Thanks.

[@martinmadsen1199]

Just found your channel, great work I very much enjoy the material covered and your style of teaching. The goal: I would like to understand the underlying cause of diffraction, in an intuitive way if possible. A video or key terms would help. Background. I work with microwave communication links and have always had problems understanding the cause of diffraction. Reflection, refraction, absorption and polarization are all quite intuitive in that a wave propagates through one material and encounters a border with another material. Each wave length may behave slightly different, but I understand why a wave behaves like it does i.e. changes direction as in the case of refraction. Diffraction just does not click for me. Simple observations like the amount of energy that ends up changing direction as a result of diffraction appear disproportionate to the portion of the wave that comes in contact with the obstacle border. Obviously it is a problem with me, but I would very much like to better understand our antenna and radio designs. It was suggested that i try considering each point along the wave front as a discrete source of spherical waves and many others, but none of it has done the trick.

[@davidc8357]

I think the quantum understanding of diffraction would help, it is more complete. Basically think of a single photon, it does interact with the slit material physically and in doing so chooses its path to the screen. In advanced experiments the diffraction pattern is observed whether we shine one photon at a time or many at a time. There are only so many paths through the slit and as Huygens showed many years ago this can be represented as a series of point sources. Similarly if you google light modes in a fibre optic you get the same limited number of modes, think of the slit as a very short hollow fibre. I've read that every photon has a predetermined path (or wavefuction) as it is emitted which depends on its surroundings. Based on your position at the screen the photons will be coming at you in phase or out of phase from the pathways. If you try and detect the photons out of phase with your eye or CCD the electrons in the silicon or nerve cell don't register the E field which is net zero. One needs to use a thermopile or 'power meter' and the photons will be absorbed and measured ( maybe due to scattering nature of the material which separates the photons).

[@rapturas]

This is no doubt a silly question, but what happens to the energy of the photons (E.ph) during destructive interference if the light is cancelled out? I can understand what happens to the kinetic energy of waves in water, but can't apply the same to photons.

[@DrPhysicsA]

It's a very good question. And it illustrates the difficulty we have with understanding quantum mechanics in classical terms. We can say that two waves are out of phase and therefore there is destructive interference. But of course we also mean that two photons somehow cancel each other out at the dark fringes.

[@rapturas]

Thank you for your response! This question has been bugging me for a while now and I've not been successful in finding an answer that I'm able to understand. I have a certificate in natural sciences through the OU so have a basic understanding of physics and quantum mechanics, but am very determined to learn. Is there an explanation to the "somehow"? I assumed it must have something to do with virtual particles/photons but reading through literature, wikipedia, and forums, I'm still none the wiser. Thanks again for your responses, it is very much appreciated! I'm a long time follower and subscriber to your channel and have used your videos to help me through studying. There are few resources that are as insightful and a pleasure to learn from as yours - cheers! :)

[@wasitnice]

What is the difference between monochromatic light and, let's say, then sun's light. Can we see the difference and how does one produce such a source of light?

[@DrPhysicsA]

Monochromatic light is light at a single frequency (colour). Whereas the light from the sun covers all the frequencies of the visible spectrum from Red through to Violet.

[@yichizhang795]

very good!

[@randomuser405]

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[@srijanagrawal1791]

THANKS!

[@MegaInformazione]

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