Comments for physicspages.com

This blog is for comments and reports of errors on my physicspages.com site. I will also post notifications of new articles published on the main site using this blog, so if you want  to be kept up to date, check here regularly, or else  subscribe to it for email notifications. I realize this may look like a roundabout way of organizing things, but I don’t trust WordPress with anything substantial any more.

If you’re reporting an error or want clarification of an equation in an article, PLEASE include:

  • The URL of the page – just copy this from the browser’s address bar at the top.
  • The equation number containing the error.
  • And of course, what you think is wrong with it.

Thanks, and I hope you find the new site as useful as the old one.

 

 

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17 Responses to Comments for physicspages.com

  1. Anonymous says:

    I believe your equation 0.7 for Shankar’s problem 1.8.9 should be the ith component of L, not the L vector as a whole.

    http://www.physicspages.com/pdf/Shankar/Shankar%20Exercises%2001.08.09.pdf

    Like

  2. Arpon says:

    I have some confusion about your solution to problem 14.05.03, Principles of Quantum Mechanics, Shankar. (Link: http://physicspages.com/pdf/Shankar/Shankar%20Exercises%2014.05.03%20-%2014.05.04.pdf )
    “Now suppose we return to the case where the first apparatus transmits only spin z of +h/2 but the second (aligned along the x axis) transmits everything (no blocked beam) into a third apparatus, which is aligned again along the z axis, but now transmits only particles with spin z of -h/2. In this
    case, the middle (x axis) apparatus has no effect since it doesn’t filter the particles at all, with the result that we’re feeding a stream of +h/2 particles into an apparatus that detects only spin -h/2. In this case, nothing will get through.”
    My opinion is: When the spin +z electrons pass through the second SG (along x axis) apparatus, the outcome is electrons in the +x and -x spin state. The state is no more +z spin. So when the +x and -x spin electrons pass through the 3rd SG apparatus (along z axis) 50% of them should get through.

    Like

    • growescience says:

      I originally thought the same thing, but I think the point is that we aren’t allowed to look at the output of the middle detector, so we don’t ever measure a particle’s x-spin. In that case, all the particles remain in the +z state, so they all get blocked in the third detector. I suspect you’re right that if we did measure the x-spin in the middle detector that would place the particle in either the +x or -x state, with z-spin undetermined, so that 50% of them would indeed get through the third detector.
      Shankar gives zero as the answer at the back of the book, so my guess is that’s what’s happening.

      Like

  3. incomprehensiblething says:

    Just to say thank you for all your work on PhysicsPages, past and present. Your site is much appreciated, but don’t overstress yourself getting it back online.

    Like

    • growescience says:

      Glad you find it useful. I’m trying to get it restored ASAP, since once it’s done, I’ll be able to get back to actually writing something about physics…

      Like

  4. Electro says:

    sir when will your answers for griffiths electrodynamics be ready. It was very very helpful and i also need it now. Your explanations were brilliant. Please we all need that fast sir.

    Like

    • growescience says:

      It will take some time for me to restore everything. In the meantime, there is an archive of the old site available which contains most of the content up to March 2017. See the physicspages.com home page for the link, as it doesn’t seem possible to insert links in comments here.

      Like

  5. Will says:

    Thank you!!!

    Like

  6. Hello. There is a web page called the Wayback Machine (http://web.archive.org/). They take snapshots of the internet at various times and store them for access. There is a nearly 100% functional version of the old Word Press site from June of this year available. I have been using it to view content. You can find it here:

    http://web.archive.org/web/20170620174446/http://www.physicspages.com/welcome-to-physicspages/

    It might be a good option to share with people until you get the new website up and running? Just an idea.

    I’m an undergrad Physics student. Three semesters to go (including this one). Your website is extremely valuable, and I thank you very much for the work you have done.

    Cheers!

    Like

  7. Danyel Cavazos says:

    Although I don’t know extremely much about web design, I have done a little before. This page is and has always been extremely useful, please let me know if I can help you in any way!

    Like

    • growescience says:

      Thanks for the offer. I think the basic design is OK – I want to keep it simple so it’s easy to maintain. The only thing that would be useful is some way of reliably displaying PDF files in the various browsers, although I suspect this might not be possible. Chrome has removed support for the Adobe plugin. On Firefox, the equals signs in the equations don’t show up. And so on and on…
      I think the best solution is for users to just download the PDFs and view them offline.

      Like

      • Danyel Cavazos says:

        What were you using to display equations before? I’m sure there are ways of presenting LaTex eqns in HTML code via extensions

        Like

      • growescience says:

        I was using the Latex “Beautiful Math” plugin from Jetpack in WordPress. I think there are Latex extensions (Mathjax?) for displaying math in HTML, but as I use the Lyx editor for writing the posts in Latex and it has a Latex–>PDF converter, it’s easiest to just create PDFs and upload them.
        Thanks anyway.

        Like

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