I need your help teaching physics

[ΔxΔp≥ћ/2]

slides 1-3,9-11,13,14,20,21,23,25-27 (wich is exacly half) are all about 10-15 seconds long
The rest is marginally longer (30seconds with very few slides around a minute)
I could easily cut about 8 slides: 3, 8, (7 or 9), 11, 18, 20, 21, 27 this is about two minutes max. This could however dilute some of the content and add more responsability to other slides.
Maybe I am just bad at evaluating time.

 

[ΔxΔp≥ћ/2]

Listen to blechman, if you do have fifteen minutes at maximum your going to have about 30 seconds a slide, do you think you can explain the De Broglie hypothesis in that time or quantum tunneling in a minute. My advice is keep it simple and keep the audiences attention, there is no point explaining a complex idea to someone that does not understand the basic principles behind it, teach them these. I would try to stick to things like the photoelectric effect and explain how in this situation the light energy is arrives or is observed arriving in discrete "packets" of energy. Maybe near the end of the presentation have one or two slides incorporating more advanced ideas but only briefly mention the outline of what these are and their place in modern physics.

The De Broglie hypothesis slide essentially says: and what if matter had wave properties (that’s it)

Although it was my original intent to talk about (and demonstrate) the photoelectric effect quite in depth, I want to skim over it as fast as possible. I would even like to get rid of it. It is a concept that could easily take a whole presentation and I don't think it presents enough QM concepts.

As for quantum tunnelling, I admit that it will be much more that a minute. However, that time is split between the uncertainty slide and slides 24-27 that are all meant to explain tunnelling and about nothing else.

The goal of my slides is to be as simple as possible, avoiding technicalities that could lead to long tangents. I want to avoid dangerous generalisations though.

I also know that I will have three kinds of people: People who refuse to accept the theory because it seems too weird, people who accept the theory because they didn’t understand and associate QM with classical concepts, and people who are in awe and slightly confused. I would like to have more of the third kind.

And by the way guys, it may seem like I refuse to take your advice or listen to you, but talking to you guys is really helping me a lot to flesh out my presentation.

If any of you know why my experiment failed, I would love to know why. I am running out of time to fix it.

As always, I greatly appreciate all the help you have given me and continue to give me.

 

[muppet]

The most simple problem I can think of to do with quantum mechanics would use the De Broglie relation:
$$\lambda=\frac{h}{p}$$
If you're talking about the two- slit experiment (which I would definitely make the focal point of an introduction to people without advanced maths skills or prior knowledge of QM) then you could calculate the momentum of the particles needed to produce a particular interference pattern- use $$n\lambda=dsin\theta$$ like in a standard GCSE problem to work out the wavelength, then de broglie to work out the momentum of the particle.
I would structure your talk as something like:
Presentation of the two slit experiment.
De broglie's explanation of 'pilot waves'
Problem
Modern understanding of what the wave is.
Although even that might push 15 mins tbh!
I know you've mentioned your teacher on here before...so be prepared to answer the questions that everyone who finds the two-slit experiment counter-intuitive to the point of offence asks: could the electrons just be bouncing off the slits, or reacting with each other in a particular way, and similar nonsenses! Be prepared (ideally) to cite specific experiments that he can go away and read about in answer to any questions you get asked.
Good luck

 

[ΔxΔp≥ћ/2]

The most simple problem I can think of to do with quantum mechanics would use the De Broglie relation

Thank you, I will use it. I was not sure whether it was as cut and dry as it seemed or still accepted as accurate. Since you have said this, I will assume that the frequency is also equal to the energy devided by Planck's constant.

De broglie's explanation of 'pilot waves'

I really want to avoid that. (long tangent, not so fundamental)

If you're talking about the two- slit experiment (which I would definitely make the focal point of an introduction to people without advanced maths skills or prior knowledge of QM) then you could calculate the momentum of the particles needed to produce a particular interference pattern- use like in a standard GCSE problem to work out the wavelength, then de broglie to work out the momentum of the particle.

I'm sorry, I do not quite see what this proves. It seems long though.

My presentation is centered around the double-slit experiment. I just want everybody to get the backround and the the concepts to understand what we think happens.

As always, thank you very much for your imput.

 

[muppet]

I don't know what country you live in or how old you are; but at school I had to solve very basic problems based on interference between two coherent sources- usually light being shone at a screen with two slits in! I may have been wrong about it being GCSE, as I can only find A-level papers on it now- see question one on http://www.aqa.org.uk/qual/gceasa/qp-ms/AQA-PA04B-W-QP-JAN07.PDF . My suggestion is if your teacher wants you to work through a problem, that you take this school-level problem, in which you would be given all bar one of the parameters n, lambda, theta and d, and use simple algebra to work out the remaining one, then substitute lambda in the equation I gave earlier for h/p to rephrase the problem in terms of QM and particles.

 

[belliott4488]

FWIW, I'll toss my 2 cents in here. First, I agree completely with blechman and nrqed: less material covered carefully and well always gets a better response than more material covered too quickly. The exception is when the presenter doesn't know what he's talking about, reads a one-minute blurb, and then has no idea where to go after that - but you've already clearly demonstrated the kind of passion that makes it likely that you'll go on and on until your teacher tells you that you're out of time - that's a good thing.

As for the experiments, I have to say that although the double-slit experiment is the "canonical" starting point for QM discussions, I've always found it difficult to get across to lay audiences. I think part of the problem is that understanding even the classical phenomenon of interference requires a certain amount of effort, since it's not an obvious part of day-to-day experience, so then going to the QM version pushes the audience past the point of comprehension, so that they miss the "oh, wow" factor. That's been my problem, but maybe you can do better.

I also agree with nrqed - I hate talking about Schr. Cat - it is misunderstood more often than understood correctly. So, my choice is blechman's suggestion of the polarizers - I've never run across that as a pedagogical tool, for some reason, but I really like it! Sort of a macroscopic example of a QM effect - sort of.

Anyway, good luck! Many of us have been in this situation - trying to pass on some of the excitement we feel about a subject - but know how frustrating it can be. I once tried to explain the interpretation of Dirac's negative energy sea to a party of drunken lay people, but I suspect all they got out of it was that I was either very drunk or very excited by strange ideas (little did they know that it was both!).

 

[David_Harkin]

I don't know what country you live in or how old you are; but at school I had to solve very basic problems based on interference between two coherent sources- usually light being shone at a screen with two slits in! I may have been wrong about it being GCSE, as I can only find A-level papers on it now- see question one on http://www.aqa.org.uk/qual/gceasa/qp-ms/AQA-PA04B-W-QP-JAN07.PDF . My suggestion is if your teacher wants you to work through a problem, that you take this school-level problem, in which you would be given all bar one of the parameters n, lambda, theta and d, and use simple algebra to work out the remaining one, then substitute lambda in the equation I gave earlier for h/p to rephrase the problem in terms of QM and particles.

HAHAHA...i done some of those questions last year for revision! lol

 

[ΔxΔp≥ћ/2]

I don't know what country you live in or how old you are; but at school I had to solve very basic problems based on interference between two coherent sources- usually light being shone at a screen with two slits in! I may have been wrong about it being GCSE, as I can only find A-level papers on it now- see question one on this paper. My suggestion is if your teacher wants you to work through a problem, that you take this school-level problem, in which you would be given all bar one of the parameters n, lambda, theta and d, and use simple algebra to work out the remaining one, then substitute lambda in the equation I gave earlier for h/p to rephrase the problem in terms of QM and particles.

I don't want to hijack my own thread, but we are taught nothing but mechanics in physics class (and I've made it to physics 3, you think we would have seen something else by now. There is one class, ph. 4 that is called EM though.), this might be a "there's no chance in hell you'll get into MIT son" program or something :-) .

Back onto subject, if my problem is not very direct or not very intuitive, no one will follow and I will lose a tremendous amount of time.

I would rather calculate the wavelength of a baseball with a certain velocity (I got this problem in a wonderful textbook that we don't use :-( ). Is that ok? Is this an appropriate way to show that the wave length is very, very short, so macroscopically, we always experience particles?

I plan on demonstrating Young’s experiment to show what interference is and then later on showing what happens when one particle at a time goes through the experiment (it still interferes, so particles can't be "bumping" each other.) In general, my presentation teaches by showing experimental observations that one could hopefully easily draw conclusions from.

I also agree with nrqed - I hate talking about Schr. Cat - it is misunderstood more often than understood correctly. So, my choice is blechman's suggestion of the polarizers - I've never run across that as a pedagogical tool, for some reason, but I really like it! Sort of a macroscopic example of a QM effect - sort of.

I want to stay as far away as possible from that darn cat.

Polarizers sound interesting, but as I said, no one has any experience with physics other than mechanics. Frankly, I still do not really understand the polarizer experiment even after the efforts of members to help me.

I would like anybody who knows why my experiment with an LED light explained in post #32 does not work and how I can fix it. As mentioned earlier, it is highly probable that I am completely ignorant about some physical property because I have no experience there.

As always thank you very much guys.

 

[muppet]

The baseball calculation would be absolutely fine. You might want to repeat it for something like a speck of dust, or something else that we think of as beng really small but macroscopic, just to emphasise how small we're talking here.
I've got to admit to being impressed by that demonstration of the HUP. The only reason I can think of is that you're talking about scales which will require a fair degree of precision and steadiness-try mounting your metal pieces in a similar way to that shown in the video

 

[ΔxΔp≥ћ/2]

I've got to admit to being impressed by that demonstration of the HUP. The only reason I can think of is that you're talking about scales which will require a fair degree of precision and steadiness-try mounting your metal pieces in a similar way to that shown in the video

If only I knew how, I don't think that I will be able to replicate that exact experimental set-up (laser, focus-thingy and that box)

When I look at the video again, it seems that my slit could possibly be smaller than his??!? As stated before, I use a wrench and the slit can get so small, that I can't see through it (a sliver of light gets through though)

 

[ΔxΔp≥ћ/2]

I just had a weird idea...

Here is part of the web page on Dr. Walter Lewin on the MIT website:

Lewin's lectures at MIT are legendary. Many have been shown for over six years on UWTV in Seattle, reaching an audience of about four million people. He personally responded to all e-mail requests he received (hundreds per year) from UWTV viewers, who varied in age from 7 to 90. For fifteen years he was on MIT Cable TV helping freshmen with their weekly homework assignments. His programs, which were aired 24 hours per day, were also frequently watched by upper-class students. Lewin is the soul of PIVoT, a video course on Newtonian Mechanics with a total of 53 hours of video clips. Additionally, his 36 lectures on Electricity and Magnetism and 23 lectures on Vibrations and Waves can also be viewed from the course's web site. Finally, his special lectures given at MIT for science teachers and for middle school students can be viewed on MIT World.

If you guys cannot help me, should I e-mail him?

 

[muppet]

Two thoughts occurred to me yesterday about your experiment:
1. Could it be that because you're not using the laser and focusing thingy that your momentum is initially uncertain anyway? So you don't notice any increase in the uncertainty as a result of narrowing your slit?
2. I don't know that the HUP explains the interference minima you can see in that video; and classical results that do that have been known since the 17th century. Unless you combined it with a presentation of the photoelectric effect, your teacher will turn around and say "So light is a wave. We knew that." So you may be better off concentrating on the wavelike behaviour of matter.

 

[blechman]

Well, while I was away, HUP, you've been getting some great advice from other people, so I feel better about not responding too quickly.

Let me say a few back comments:
1) If a slide is only "10-15 seconds long", then it is not worth having! Drop it completely! Rule of thumb: design your slides to be 1 minute each. So you should plan on no more than 15 slides on the outside.

2) As has already been mentioned by muppet, I'm not sure what your version of the slit experiment proves. All waves will behave this way (it's called "diffraction") and you don't need Heisenberg to prove it - it was known about since Newton's day! It **IS** true that there is an uncertainty relation from wave mechanics, sometimes called the "classical uncertainty principle" by textbooks, which can be used to justify this behavior, but again, it's not Heisenberg (well, of course they are related, but you don't need Heisenberg to see the effect is all I'm saying).

Where the QM comes in with light is when you lower the INTENSITY of the light - then you see that there are individual "dots" on your screen proving that light must be made of particles. Then you can do Young's double-slit experiment to prove that light must be made of waves. And then your head explodes!

Unfortunately, I do not know of a way to lower the intensity of light to that extent with equipment available in a high-school classroom. Maybe someone else has a better idea?? (This is the problem when you ask a theorist for demo ideas! )

The only thing I can think of is for you to do the double-slit experiment with light (that should be easy enough) - which by itself might not be called a "quantum experiment" since it's predicted by CLASSICAL E&M, and then SAY to your audience that when the exact same experiment is repeated with neutrons rather than light, then you see the same thing, thus "proving" that neutrons are waves! Apologize that your budget does not allow for you to acquire a neutron source, but that you will be accepting donations from any skeptics so you can prove it to them!

You can also use words to describe the quantum nature of light as I mentioned 3 paragraphs up.

This has little to do with HUP (at least directly), but there you are.

 

[ΔxΔp≥ћ/2]

''1) If a slide is only "10-15 seconds long", then it is not worth having! Drop it completely! Rule of thumb: design your slides to be 1 minute each. So you should plan on no more than 15 slides on the outside.'' Most of those slides where just picture slides, transition slides or just associated with other slides. I took your advice anyways and cut down on quite a few.

''2) As has already been mentioned by muppet, I'm not sure what your version of the slit experiment proves. All waves will behave this way (it's called "diffraction") and you don't need Heisenberg to prove it - it was known about since Newton's day! It **IS** true that there is an uncertainty relation from wave mechanics, sometimes called the "classical uncertainty principle" by textbooks, which can be used to justify this behavior, but again, it's not Heisenberg (well, of course they are related, but you don't need Heisenberg to see the effect is all I'm saying).''
I have become aware of this. However, I believe that if we explain the experiment with photons, the HUP is necessary. I will say something like ''electrons and neutrons do this too''.

''The only thing I can think of is for you to do the double-slit experiment with light (that should be easy enough) - which by itself might not be called a "quantum experiment" since it's predicted by CLASSICAL E&M, and then SAY to your audience that when the exact same experiment is repeated with neutrons rather than light, then you see the same thing, thus "proving" that neutrons are waves! Apologize that your budget does not allow for you to acquire a neutron source, but that you will be accepting donations from any skeptics so you can prove it to them!''
I have already prepared the equipement to do this demonstration. Thanks for the budget joke, I will use it.

''1. Could it be that because you're not using the laser and focusing thingy that your momentum is initially uncertain anyway? So you don't notice any increase in the uncertainty as a result of narrowing your slit?''
I have two hypothesis. One is that the wavelength of the light is too long (my LED is green). The other is that the slit is still too narrow.

I have e-mailed Walter Lewin on this subject and his response was so quick that it was scary (no more than 15-30min). He has sent my e-mail to his demo guru.

As always, thanks for the help guys. I will be on vacation until next tuesday. My dad wants to run the Pheonix marathon. It will be a good time to catch up on my P. A. M. Dirac and to do homework. I will have three oral presentations and four tests to do when I get back, not to mention exams the week after. So don't expect answers to any of your posts until then. I will probably be presenting my project on quantum mechanics thursday and the one on special relativity in two classes probably the same day.

 

[muppet]

Neither of your hypotheses works I'm afraid. Diffraction works best when the size of your slit is comparable to the wavelength of your light (and here we're talking a few hundred nanometers). So a long wavelength and a narrow slit should actually help! The only reason you see red light used in these experiments so often is because that's the kind of laser it's cheapest to make.

 

[blechman]

I will be on vacation until next tuesday. My dad wants to run the Pheonix marathon. It will be a good time to catch up on my P. A. M. Dirac and to do homework.

you sure do have a fascinating choice of bedtime reading, I must say! There are parts of that book that I *STILL* don't understand, and I've been studying the subject for years!

But anyway, once again, good luck on your presentation. I'm sure you'll do fine. Have fun!

 

[ΔxΔp≥ћ/2]

I'm back!

Let's see if one can really make a long story short:

Phoenix > Home
Phoenix: great drivers, great weather, holy moly that fashion park is huge, Grand Canyon is a hole in the ground
Snow storm @ home, slept in an airport
Came home

I got a response from Markos Hankin. He is among other things a demo guru at MIT. He told me to get a laser pointer because the light has to be highly directional and of single wavelenght. He also told me to attach single edged razor blades to the wrench. I hope that I will be able to get the stuff and try it out tomorrow.

Neither of your hypotheses works I'm afraid. Diffraction works best when the size of your slit is comparable to the wavelength of your light (and here we're talking a few hundred nanometers). So a long wavelength and a narrow slit should actually help! The only reason you see red light used in these experiments so often is because that's the kind of laser it's cheapest to make.

I'll try to make my laser violet then.

I probably will not go to school tomorrow, I have too much homework to sort out. I also have tests and presentations to prepare for.

 

[belliott4488]

I'll try to make my laser violet then.

I probably will not go to school tomorrow, I have too much homework to sort out. I also have tests and presentations to prepare for.

You can get a violet laser? I've never even heard of one, let alone seen one! Sounds very cool if it does exist, though.

If you're doing diffraction, keep in mind what others have said: the wavelengths for visible light are on the order of thousandths of a millimeter, so the way one usually demonstrates diffraction is with a diffraction grating, i.e. a mirror with precisely engraved grooves in it.

 

[LongOne]

Suggest a demonstration of the Casimir effect.