Waves - A Level Physics

[@johnmontgomery560]

I love your lectures. When I retired I was considering going back to university to study physics. Now I can do it at home with a superb lecturer John

[@candleinthewind9135]

I can't believe nobody's commented on how awesome his accent is yet.

[@robertfinkle9020]

+candleinthewind "something to add about the CURRENT!"

[@cowardlyheroine]

+candleinthewind He sounds a bit like Baymax? I'm only saying this because I watched Big Hero 6 recently :)

[@yesiamadorito]

OMFG IT WASN'T JUST ME

[@ToDie4r]

true, it plays big role in making us understand better

[@parksliderbarricade4324]

He reminds me of my Further Maths teacher. He's so enthusiastic and it's beautiful.

[@DrPhysicsA]

I am magnifying the whole slit so it is of length d. The argument is that in the circumstances I describe, you can think of the slit as being of two halves (each of d/2). Light from any point in the top half will be exactly out of phase (ie will cancel out) light from the corresponding point in the lower half. So all the light from the top half cancels the light from the bottom half (at the angle theta).

[@sandorclegane2485]

I've never heard a clock that goes "mooo". Fascinating.

[@yaseenahammed6352]

Sandor Clegane I will eat every chicken in this room.

[@finlaykingdon2063]

hes British dont be racist

[@missabcgirl123]

learnt more in 36 minutes then i have in the entire year

[@Benjones96]

Glad im not the only one xD

[@DrPhysicsA]

I hope it has proved helpful in any exams you may have been taking.

[@krcd-eb6kb]

Beth Jackson agreed

[@ToDie4r]

exactly :)

[@nataliaperez9372]

me right now

[@annepioquinto4784]

Exam is tomorrow and I'm ready to go! Thank you immensely for making such digestible videos!

[@DrPhysicsA]

Thanks. Hope the exam went well.

[@TheRealWorld-TateSpeach]

What did you get?

[@johnpaul4301]

@@TheRealWorld-TateSpeach he failed with flying colors

[@hadeedahmad9465]

@@DrPhysicsA can you tell me how much this video covers the cie alevel waves topic? Does this leave anything out that is in the cie syllabus?

[@snhtsljedc9803]

Hadeed Ahmad do u still need an answer?

[@deebarfield2633]

Loving the fact there's so many people watching these videos as last minute revision! They're so informative and everything is explained really well! Thank you :-)

[@DrPhysicsA]

Thanks for your kind words. Glad they have been on some help.

[@walshamite]

This series is GREAT. At school (1960s), did General Science, ), not enough physics there. Following hobby of astronomy-cosmology, I've been aware of gaps needing knowledge. Using YT physics clips to fill my gaps. Kinda knew some of it, but back to basics makes me see relationships as never before. I can follow the math. In my 60s now, still love steep learning curves. I learn better these days, no exams, just the joy of knowing. Thanks a 10 to the minus 6. It's a joy. UR never 2 old 2 learn!

[@DrPhysicsA]

Much depends on where you draw the x axis. A trough isn't usually defined in that way. A trough is the point at which the wave reaches its lowest point on the y axis, just as a crest it where the wave reaches its highest point on the y axis. Eg y = sin x

[@ARaven5]

woah, my physics exam is next week and this has helped me a bunch! amazing video, thank you!! (much better than my teachers:P)

[@DrPhysicsA]

Thanks. And all good wishes for the exam.

[@NTye]

This was brilliant, like having a revision lesson without being at school! But a lesson I can pause, rewind etc as often as I need to. I was really struggling with standing waves, but you've helped me, thanks a lot!

[@DrPhysicsA]

Lamda is defined as the wavelength - ie the distance between consecutive peaks in the wave. Frequency is defined by the number of wave peaks passing a point per second. The speed of the wave is the product of the two.

[@alext9067]

I like the clock mooing. I will also add that these videos are of tremendous interest to me and that I appreciate your effort and your candidness in presenting them.

[@DrPhysicsA]

Well spotted. Its a cuckoo clock with a cow instead of a cuckoo!

[@els257]

Thank you, I am an A* Student and I have been struggling a lot with this unit and this has really cleared a lot of things up for me. Thank you so much for your help!

[@DrPhysicsA]

Thanks for comment. I'm not really sure what the benefits of polarisation might be. Google suggests some. But polarised glasses will reduce the amount of light entering the eye and can also reduce reflected sunlight (glare) which is itself polarised.

[@MathPhysicsFunwithGus]

Your videos are amazing! I am first year undergraduate physics major and I proved that e&m waves travel at c after watching your videos and I understand the whole derivation and proof and can do it on my own no problem! Thank you!

[@DrPhysicsA]

You are quite right. Its a moot point whether that counts as internal reflection. But as you say, beyond the critical angle it certainly is internally reflected.

[@heidigarbett97]

youve genuinely made everything ive been taught in class become clear to me now

[@pico5746]

I've just started A-levels but I need to do really well so watching these early on should help with revision later on as i'll just need to recap

[@DrPhysicsA]

All good wishes with your studies.

[@akshaypetta]

This is probably the best thing to happen to KZbin. Thank You.

[@DrPhysicsA]

@SailaMaham Yes that is exactly what happens. On a screen placed a few metres from the slit you will see an intense blob of light in the centre fading to a dark fringe then it become light again, then dark, although the flight areas become significantly less intense after that.

[@DrPhysicsA]

A good way to understand phase difference is to consider two waves with the same frequency, wavelength and amplitude which start out at different points. How far is the second wave behind the first one? You could give the answer in terms of distance - but that wouldn't tell us very much. We could give the answer in terms of wavelength. So if the second wave was half a wavelength behind then the two waves would be completely out of phase. Or you could regard each wavelength as 1 cycle = 2 pi rads

[@mdk124]

Really appreciate your effort going through all this! Not sure if i could have talked about physics for 30 over minutes!

[@DrPhysicsA]

Not sure I can do that at present, but I see from the internet that there are ways of downloading from KZbin for later viewing in the style of a podcast.

[@DrPhysicsA]

This can get very philosophical. The speed changes and there is a compensating change in wavelength such that c=λf, but f itself does not change. The energy of the photons do not change (since E=hf). But the key point is that in order for you to see the colour the light has to leave the medium (glass, water etc) to travel thro your eye to your retina. So the only real sense of colour is that which is determined by the wavelength and frequency of light in your eye as it hits the retina.

[@DrPhysicsA]

Path difference is just a measure of how much out of phase one wave is with respect to another. It can be measured in terms of wavelengths. But the key point is the fraction of a wavelength by which one wave is out of sync. This can be expressed either in terms of wavelengths of radians (2 pi rads = 1 wavelength). Frequency doesn't really afffect path length. No matter what the frequency two waves can be out of phase.

[@DrPhysicsA]

Because for a small angle the hypotenuse and the adjacent are almost equal. So for small angles sin theta is the same as tan theta in terms of significant figures.

[@DrPhysicsA]

sin r = 1 at the critical angle. This is the angle at which the angle of refraction is 90 degrees (ie along the surface of the water/glass). sin 90 =1. Beyond the critical angle, all the light is totally internally reflected.

[@DrPhysicsA]

At 21:00 I am showing a particular light wave which is at angle ϴ (ie the angle which will produce a dark patch on the screen). This means that at that angle, the light waves reaching that point on the screen are canceling each other out. Geometry relates ϴ, d and λ. So we show what the condition is for light waves to cancel out.

[@fatimaposwal7894]

Thank very much Sir! I respect teachers because they teach you what they love teaching and only those who have a passion to teach others teach to a good standard. May God guide you and be with you. Best wishes, physics student

[@DrPhysicsA]

And you could then express the half a wavelength in terms of radians (ie pi in this case).

[@DrPhysicsA]

Think of it in terms of photons. The energy of a photon E = hf (where h is Planck's constant and f is frequency of the light). If f were to change then there would be a change in energy. Where would the energy gain/loss arise?

[@DrPhysicsA]

The gap thro which the wave passes has to be broadly the same size as the wavelength. That's why sound "diffracts" through a door but light doesn't.

[@jorgegonzalez-ec5fl]

This guy really knows what he's talking about. I'm glad we still have real teachers out there.

[@sandlertossone1813]

Would love to hear a lecture on transmission line theory. Most video's online are not very helpful. I have watched almost all your videos and can say learned something new in each one. You have a special gift of taking complicated theory and relaying it simply to the everyday person.

[@DrPhysicsA]

It covers material in the AQA, OCR and Edexcel syllabus and I have also added some material from the CIE syllabus. I cant guarantee that it covers everything. If anyone spots gaps, let me know and I'll try to add more videos to cover them.

[@bigrockets]

most excellent presentation on waves, angles of incidence , refraction and reflections. Well done!!!

[@Jood9090]

I like the way he explained!! I need this man guys!!!! he's explaining better than mt teacher, I feel that he's is understanding what he's saying not like the other only say what they know and he also explain slower. really I like this man!! and I need him also!

[@DrPhysicsA]

If 2 waves are not in sync, then ask yourself by how much of a wavelength (or cycle) one lags behind the other. So suppose it is a quarter of a wavelength. Then you know that 1 wavelength = 1 cycle = 360 degrees = 2 pi radians. So now you can express the phase diff in degrees or radians or wavelengths. Where do I say n=1/2lamda?

[@DrPhysicsA]

Thanks. I have done a number of videos with example exam questions from the various A Level courses.

[@donaldcambridge1040]

life saver. awesome video man

[@pufalupagus]

Great job i'm 16 yrs old and i understand this perfectly. Watching your lectures is a great pass time of mine

[@DrPhysicsA]

Well frequency is one divided by the Period (T). T is measured in seconds. Frequency is measured in cycles per second. So frequency tells you how many cycles or wavelengths pass a particular point per second. T tells you how long it takes one wave to pass the given point.

[@DrPhysicsA]

There are various ways photons interact with matter, but the key one for the issue you raise is that some photons give up all their energy as opposed to a partial loss of energy by all photons. For example a photon might transfer its energy (E-hf) to an electron and liberate the electron from the atom with an excess of Kinetic Energy that is eventually converted to heat energy. The photon beam would then be less intense but photons which had not interacted would retain their original energy.

[@ucingtigatiga]

i agree,DrPhysicsA have great method explaining physics,to the point theoretically yet still engage intuitively.please expand your teaching by give problems to solve mr DrPhysicsA !

[@DrPhysicsA]

Yes you rightly make the point that photons travel at c only in vacuum (and more or less in air). But slower in denser media.

[@DrPhysicsA]

It's all down to quantum effects. Low energy photons (visible light/UV) tend to give up all their energy to an electron. Higher energy photons (in the X ray region) can show the Compton effect whereby they do give up only part of their energy to the electron and then recoil with lower energy (and lower frequency). Very high energy photons can give rise to pair production (eg electron-positron).

[@parksliderbarricade4324]

Just found this channel recently and this is perfect for getting a good grasp on Physics. Luckily, Physics is Linear so given I get a pass, I can use these videos to boost my grade greatly.

[@DrPhysicsA]

I assume you mean something like a sound wave. A sound wave propagates as a longitudinal wave by causing oscillations in the air which unlike transverse waves results in air molecules being pushed back and forth creating areas of compressed air and rarefied air which are constantly changing.

[@DrPhysicsA]

n is an integer 1, 2, 3 etc. It is the number of the fringe (ie bright spot) from the centre. You can have as many fringes as can be fitted into the formula nλ/d = sin ϴ. ϴ can never be more than 90 degrees.

[@SkiGav]

Mate, ur the absolute best! love your videos and i really really appreciate what you're doing for everyone out there!

[@DrPhysicsA]

It's already there. See my video on "Geometric Optics - A Level Physics". Go to my KZbin home page and select the A Level Physics playlist (on right hand side). you'll find it half way down.

[@bryonycoombs1018]

BLESS YOU SIR I UNDERSTAND AND 2 DAYS BEFORE MY EXAM

[@DrPhysicsA]

Thanks. Hope the exam goes really well.

[@MrKraftyy]

OCR Electrons waves and photons? lol

[@longdragon3]

MrKraftyy can't wait for it. lol

[@MrKraftyy]

karan Naga lol i can wait, done it last yr and got a C. Ive been focusing on a2 so just started recaping yday lol

[@dalemcmahon123]

Thanks again. It makes sense now!!! The photon has to pass through the eyeball to reach the retina. The eyeball is gelatinous and will further slow down the light and change the wavelength depending on the refractive index of the eye material so it doesn't matter on what type of medium that the photon has to travel through before it reached the eye. Thanks a lot for replying!...........I have got it ! eureka !!

[@phynos8936]

Wonderful video. Thank you.

[@DrPhysicsA]

Thanks. Do you mean at 7:09? If so, I have put a text comment on the video to say that it should be r squared.

[@jessicawhitney2074]

I'm woefully unprepared for my resit tomorrow, this series of videos has helped a lot :) thank you for making these

[@DrPhysicsA]

Jessica Whitney all good wishes for the exam

[@DrPhysicsA]

Many thanks. Hope it starts to make sense soon.

[@DrPhysicsA]

The velocity of a EM wave changes in different media. Since frequency remains the same the wavelength must change. A beam of light which could be regarded as a wave, has millions of photons. But if you are talking about representing subatomic particles as waves rather than particles then the particle is itself also a wave. Each particle is also its own wave.

[@DrPhysicsA]

I'm not sure which exam board you are doing but my A Level Physics playlist should cover all the material you are likely to need. I also have a series of 7 videos on electromagnetic waves in the Electricty and Magentism playlist starting with "What is light?" but that is likely to be more advanced than you will need.

[@AmitMusicProductions]

Sounds like the exam solutions guy..

[@cadkls]

You draw such beautiful waves.

[@DrPhysicsA]

They are permittivity of free space and permeability of free space respectively. I haven't done separate videos on them. For A Level it isn't necessary to know the detail of these constants.

[@Benjones96]

you have saved my life.. and for that i am eternally grateful... exam tomorrow and found these vids which have cleared up so much! thank you! :D

[@DrPhysicsA]

Hope the exam goes really well.

[@DrPhysicsA]

Thanks. There's a brief reference to how lasers work at the end (18:30) of the video on "Atomic Structure - A Level Physics". Hope that helps.

[@DrPhysicsA]

My A Level Physics playlist covers all the material that I am aware of for the main Board's British A Level syllabus (apart from some biophysics material) - although these videos are revision material and not a substitute for A Level teaching.

[@niharikags6129]

Very Well Explained!! You are very good teacher! You have made difficult concepts much easier to understand! Hats off! Thank you!

[@DrPhysicsA]

Sorry about that. What we are saying is that as light passes through a double slit it will form a pattern on the screen which is a series of alternating light and dark patches (a series of black and white stripes if you like). These are called fringes. We usually call each light stripe the fringe and the distance between any two fringes is the distance from the peak whiteness of one to the peak whiteness of the next.

[@DrPhysicsA]

I see some have responded already on this. As they say, EM waves all travel at the speed of light. The difference is their wavelength and frequency. But the produce of the two is always c. The more general answer is that EM radiation consists of massless photons whose energy is E=hf. All massless particles must travel at c. They cannot go slower, or faster.

[@DrPhysicsA]

The idea is that every point along the slit is a source of light so every point generates a light ray (the Huygens principle). I drew in the ones at the top and bottom of the slit and one in the middle. Then I show that every light ray in the top half exactly cancels the corresponding ray in the lower half.

[@asthav3000]

Thank you soo much for these videos!! I really appreciate it, you've helped me a lot!

[@shaahashareef8868]

You are much better than any teacher in school. Thank you so much sir. You are awesome! 😊😄

[@DrPhysicsA]

Thanks. Glad the video was of some help. Good luck with the future exams.

[@DrPhysicsA]

Delighted to hear that. Keep going for that A!

[@laantful]

Sir im an international student doing a levels in UK. i find it hard to learn in class bcs of the fast phase the teacher is teaching and its hard for me to understand his strong accent. but your video have helped me a lot through physics. Thank you so much. God bless.

[@artemisangelique]

is it too much to ask to make a diff playlist for As and A2? :c

[@davidpenn4024]

Yes.

[@tanharahman9737]

Artemis Angelique you might have already finished your A levels XD

[@dormantformant]

Thankyou! Your videos have helped me with my exams this january, and im sure they will help further for my exams in june aswell!

[@DrPhysicsA]

To you and all sitting the exam today, all good wishes.

[@bq1499]

You're a GENIUS! You have helped me understand things I thought were impossible to understand. :D If you have time, I hope you start to go through Exam papers one by one to give us a more fundamental idea of everything in its application. Edexcel Papers and so forth. Once again thank you very much. :)

[@DrPhysicsA]

I'm not sure. I make videos of A level subjects which should cover material in most syllabuses. But I'm not sufficiently aware of the material required for each individual exam board.

[@madamai123]

Thank you for all the videos you are uploading, i am finding them very helpful for my As physics course

[@nathanbrown492]

34:17, Is it total internal reflection if the angle of incidence is equal to the critical angle, or just if it is larger than the critical angle?

[@HasanZobaer]

Sir, you deserve more subs than pewdiepie !

[@seanki98]

Hasan Zobaer Amen

[@alwwqe]

lmao

[@lightseeker2349]

Every intellectual's utopian fantasy

[@mattbike1]

I managed to get a B in my mock for this, and ive been told i should expect a D/E. Thank you, ill keep trying for the A :)

[@DrPhysicsA]

Are there any particular issues you want covered?

[@DrPhysicsA]

Yes. At 11:55 I is proportional to 1/r^2 because P/4pi is a constant

[@DrPhysicsA]

Well it probably depends on the syllabus you are studying. But if your teacher didn't cover it in your course then its probably not in your syllabus. Can you check with any of your fellow students or teacher?

[@marianthejuniorscientist6422]

Really great resource for students as well as teacher ...

[@alphie10]

@DrPhysicsA Brilliant videos!!! My mechanics exam went fabolous i made a few silly errors on some of them but hopefully iv got that magical A that i want haha! If it wasntfor your videos dont know what i would do you cover things sometimes that my teachers dont and it gives me a better all round knowledge fantastic stuff! Thank you!! Now i gotta watch ur videos and Study for the Electricity and Waves exam

[@rachelbarn6011]

You are God sent sir! Thank you so much for these videos

[@quantum3280]

Love watching these in 2020 quarantine

[@aki957]

Thank you. Now has a better idea of what chapter wave is about.

[@Verbalbangz]

By playing these over and over in my sleep i hope to remember it

[@DrPhysicsA]

Good luck with the A Levels. I assume you have found the full A level revision playlist on my channel.

[@DrPhysicsA]

I don't think polarisers need to be used. See my video on Atomic Structure - A Level Physics where I describe how lasers work near the end.

[@DrPhysicsA]

All to do with harmonics. A trumpet and violin each playing middle C will produce the same fundamental (256 Hz). But they produce different harmonics each with different ampltudes. The C will be dominant but the harmonics affect the overall tonet. if harmonics were of the same strength as the fundamental you would hear a chord. But they are much less so you hear a different tone. Some composers try to achieve a similar effect with one dominant instrument and others playing harmonics at pppp.

[@RedfernModelRailway]

Thanks for this. My physics teacher isn't the best (or i might be a bit slow still after the holiday :/ ) and you've helped to patch up some of the gaps he left me with!

[@kylefan7237]

Wow, thank you so much for this video. It got the extra marks for me a great student from a good student. Could've scored a high B, but got carried into the A range with your video. Very informative and helpful! :)

[@jzhen92]

Life just became more simple after this video! This guy is my glitch to pass physics this year :P