The Sum over Paths Theory - A Level Physics 

Thanks for kind comments. I'm not a great fan of the phasor approach. I didn't do a video till it was requested. It rather oversimplifies what, as you say, is a much more complex approach, and in my view causes more confusion than enlightenment at this level.

you should sell the papers you draw in e-bay. A way to donate you for giving us so much free and correct knowledge!

Oddly enough, I think i understood most of it. Lack of clear definition of terms at the end had be a bit fuddled, but, was holding on all the way through!! Nice, simple explanation

excellent, very informative, and much appreciated, keep em coming PLEASEEEEE

Thank you professor. Your explanations are clear and amazingly comprehensible.

I guess its because the imperfections are not sufficiently serious to wreck the basic principle. You'll recall that the phasors from all other routes don't fully cancel out but are negligible in their contribution. As long as the imperfections don't seriously impede the image, all is well.

i swear doc u can never imagine how much thankful i am for ur help that enabled me to achieve what i always dreamed of u are a damn hero

Agreed. You are amazing, and I would very much love the ability to support you.

Thanks for your great videos! You said that the various paths through a lense to the focal point take the same amount of time and therefore all phases in the focal point are the same and add to a maximum amplitude, which square is the intensity. But real lenses are not perfect: A variation of the thickness of the lense in the middle of just 10^-6 m causes a phasedifference of about 2 Pi (by green light with lamda=530nm) Nevertheless real lenses work, why? Thanks for all answers!

your phasor graph @ 5:00, some how I don't understand why the arrows are pointing opposite to each other on the first half cycle but on the second half cycle they are all pointing down the same way

As a non physicist I recently read that book and found it very interesting. How precisely did they botch it in your view?

Very helpful :)

thanks doc.

Thank you!

I have a question, when a quantum cancels the other as a trough meets a crest where does the photons energy goes?

thank you so much

Great vid Doc, please do more of this phasor stuff. I think this is what that joker Brian Cox was trying to use to explain QM in his recent book, "The quantum universe," but he botches the whole approach...that book SUCKS! You explain it alot better. Also, do the phasors have to do with the complex conjugate wave function thing that gets canceled out by mutiplying it by the real wave function, [psi*psi]^2. Or is that something else?

one question, how can the probability be greater than one?

Thanks for the video, but it's a bit weird that you don't explain the idea of a 'phaser' before using it, it makes the explanation rather unintelligible to me.

shortest path is not the quickest paath doc