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What should I have learned in Modern Physics?

  1. May 6, 2012 #1
    My final exam is in 5 days.

    Our professor informed us that he would not test us on Chapter one which is your Lorentz transformation, length contraction, basic relativity stuff.

    But then we go all the way up to I believe chapter 7, so 6 chapters.

    The thing is, we go into Psi wave functions, talking about energy levels, the "infinite well" I'm not exactly sure.

    I barely understood the bohr electron model, as far as the energy levels and concepts such as the positronium (I understand the whole idea of it being unstable, decaying quickly, similar to the Hydrogen atom) but other than that...

    I was terrible in the energy and momentum conservation, both seen in Particle collisions as well as compton effect.

    Could someone touch up on that?

    Really I would like to get hints on what to focus on, I'm hoping that the class has general "teaching objectives" that are almost universal to other Universities.

    Also could someone touch up on radiowaves bouncing off of water and how to calculate the time it would take to detect an approaching ship from a radar station... very vague I know but I have only learned bits and pieces of each subject.

    As you can probably tell, I am a poor student, not dumb, but un-focused.

    Any help would be appreciated.
  2. jcsd
  3. May 6, 2012 #2

    Ken G

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    Gold Member

    You are asking too much-- most of the examples you give draw not just from modern physics but from physics as a whole, topics you need to have been learning for about two years now (conservation laws, how to calculate times of flight for a known speed, how to solve ordinary differential equations). You are not going to learn all those things in five days. Can you focus your question onto something more specific? As far as "teaching objectives" goes, in my view the main goal of "modern physics" should be to learn how physics itself has changed in the last 100 years or so, which means, how we have changed the way we think about space and time (relativity) and what we can know about a particle (quantum mechanical uncertainty relations). So I'd say you need to step back from the details of the list of problems you mentioned and just ask yourself, what can we know about a particle and how can we know it? That brings you into contact with the concept of probabilities (and probability amplitudes, which are called "wave functions" oftentimes when they refer to probability amplitudes of finding a particle near a given location x). A lot of quantum mechanics is then about solving for the form of the wavefunction in various situations, such as the infinite well ("particle in a box"). You should definitely start there and understand what we are allowed to know about a particle in a box, what things we cannot simulataneously know about such a particle, and how to connect these measurable things with their wavefunction (a classic example being, what are the allowed wavefunctions of a particle in a box that has a definite value for its energy). If you can understand how to show that a particle in a very tiny box must have a very large energy, then you will be well on your way to understanding modern physics, though this is of course just one example.
  4. May 6, 2012 #3


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    Staff: Mentor

    That doesn't tell us much without knowing which book you're using, or at least the titles of the chapters.

    You really should ask your professor about that, or maybe his teaching assistant if he has one. Even with more-or-less "standard" courses there's enough variation from one professor to another that it's dangerous to generalize. With an intro modern physics course I suspect there's more variation than in some other courses, because a typical book for that course covers a wide range of topics. Sometimes the course includes blackbody radiation, sometimes it doesn't. Sometimes it includes basic nuclear physics, sometimes it doesn't. Sometimes it covers multi-electron atoms and the periodic table, sometimes it doesn't. You get the idea...
  5. May 6, 2012 #4
    Are you friends with anyone in the class? or even just a "facebook" friend? I suspect you would be able to best maximize your studying efficiency if you got a handle on the scope of the class and the things the prof focused on. Does your professor post lecture powerpoints online? Is your syllabus very detailed? It is difficult enough to cram for a physics test you are unprepared for in 5 days without the added difficulty of not being sure what material you need to have mastered and what you don't...
  6. May 7, 2012 #5
    Well to give a breakdown of what we were tested on so far

    *Lorentz transformation (does the snake get cut in half by the two falling knives)

    *Lazer exiting from a gun travelling at relativistic speed (combination of Lorentz and Contraction)

    *Four particles collide, using the E^2 = (pc)^2 + (mc^2)^2 equation find the momentum and energy of some particle

    *Compton effect, photon bounces off of electron (not literally) but, after wave is 25 degrees from initial path of light etc...

    We did cover blackbody radiation in both my Modern and Thermo class, we did not cover the periodic table.

    I am not a really bad student per se, I mean I am one of the few that actually tries their homework on their own, sure I get 40's out of 90's (hw grades) but I didn't use cramster which shows you solutions.

    I do want to learn in fact my role models are "Tony Stark, Howard Hughes, Burt Rutan" yeah fictitious on the first one, crazy on the next, but... I do care but I am not exactly possessing the mentality of a college student yet

    Sorry to come off as an arrogant **** but you know... I do plan on pioneering new technology and not just getting "a job" as most college kids tell me.
  7. May 7, 2012 #6
    The book that my class used is
    Modern Physics
    For Scientists and Engineers
    Second Edition

    John R. Taylor * Chris D. Zafiratos * Michael A. Dubson
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