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  1. J

    Desperate for astrophysics help

    The energy generation rate for p-p fusion has an approximate dependence on density and temperature given by: E= e (p/pc)(T/Tc)^4 i don't know how to write all the symbols so in the above: E is epsilon, e is epsilon at the centre of the star, p is the density, pc is density at the centre...
  2. J

    Spectra Troubles

    I have tried working on this the last few days, but have been unable to decide what is going on. I know there must be an easy way to do this, but for some reason i am stuck. Any help? Thanks
  3. J

    Spectra Troubles

    Consider the Lyman photons for Hydrogen-like atoms with Z greater than one. Which of these atoms have Lyman alpha photons in the 1)visible 2)UV 3)X-ray and 4)gamma-ray parts of the spectrum? Can list ranges of values of Z in the answers. My thoughts are to use 1/lambda=...
  4. J

    Absolute zero founder

    sorry don't know much about Wikipedia. is it reliable? you know how you can't be sure of some of the things you read online.
  5. J

    Absolute zero founder

    This is a pretty straight forward question. Does anyone know who exactly first determined the value of absolute zero and when it was. I am getting conflicting information about it. this is not a question i have to answer, just a little bit of information i would like to include in a physics...
  6. J

    Astrophysics - Can there be a contact binary from white dwarfs

    Question: A typical white dwarf has a mass of 1 solar mass and a radius of 10 thousand km. A typical neutron star has a mass of 1.5 solar masses and a radius of 30km. Given that there's a natural speed limit in Nature, namely the speed of light, is it possible to have a contact binary...
  7. J

    Integral help

    just wanted to let anyone who helped out with this know that my friend and i figured out, by looking at the derivative of the answer the prof gave, that there is a typo in the original question. it should not be 5x^3 (1+x^2)^1/2, but 5x (1+x^2)^1/3. it was written in such a way that i don't...
  8. J

    Integral help

    sorry Gamma, missed your post about the answer being wrong. glad to here that i am not way off base on this. thanks all for your input
  9. J

    Integral help

    does anyone agree with me that maybe the answer given by my friend's sheet is incorrect?
  10. J

    Integral help

    sorry, but i'm not sure how your answer is equivalent to the answer she was given ie)15/8(1+x^2)^4/3 +C. also, i guess i wasn't clear in my last post. they haven't done trig subs, by parts, partial fractions, etc, nothing like that yet. all they have done is u subs. this isn't even my...
  11. J

    Integral help

    wow. that is unlike either answer i posted. i guess i should have stated that the only special way they have learned to solve integrals is with a u sub. did you see what exactly i did wrong in the way i tried to solve it? sometimes one needs an extra pair of eyes to find the error.
  12. J

    Integral help

    this should be easy, but i'm struggling. i'm trying to help a friend solve: integral(5x^3(1+x^2)^1/2), sorry i don't know how to do the integral sign. i did a u sub with u=1+x^2, du=2xdx and u-1=x^2 so: (5/2)integral((u-1)(u)^1/2) i get (1+x^2)^5/2-10/6(1+x^2)^3/2 +C the...
  13. J

    Theory question

    this is probably a stupid question, but what exactly qualifies as macroscopic ie)what is the actual range? also, i get the question now. it was much simpler than what i was trying to make it out to be. thanks for the imput. you physics guys rock.
  14. J

    Theory question

    so the size of macroscopic objects is much larger than what the uncertainty in their positions. i'm not sure what this means in regards to quantum mechanics. i find quantum physics so confusing and i highly respect anyone who understands and enjoys it.
  15. J

    Theory question

    i have a question where it asks me to find the uncertainty in a ball's postion (m=50g). i have that part all figured out, but then it asks me what the answer indicates about the relevance of quantum mechanics to macroscopic objects. (the answer was approx. 10^-32m, a very small uncertainty)...
  16. J

    Double slit electron experiment

    isn't dsin(theta)= (m+1/2)lambda for the dark fringes of the double slit. how do i know to use this instead of just dsin(theta)= mlambda? also, again, i don't understand where you got the tan equation. it has been a very long time since i did anything with diffraction, and i have one of...
  17. J

    Double slit electron experiment

    i have no clue as to where you came up with dsin(theta)=(m+1/2)(lambda) also what does the tan equation mean. i need some help to understand what is going on. what is delta y? i am so lost on this topic. any layman's terms explainations would be so appreciated. thanks.
  18. J

    Double slit electron experiment

    i think i understand what you are saying for c). the text describes a similar situation, where the detecting particle has uncertainty in its momentum and postion. through calculations they determine that for the dectecting particle: (delta P)(delta y) < h/2. this is a clear violation of HUP...
  19. J

    Double slit electron experiment

    A monochromated beam of neutrons (speed 0.40 m/s) is directed through a double slit with 1.0 mm separation. An array of detectors is placed 10m from the slit. a)what is the de Broglie wavelength of the neutrons? b)how far off-axis is the first zero-intensity point on the detector array...
  20. J

    Physics HUP help

    i just realized that i kept repeatedly using the same wrong number to figure out the other question. now i get it exactly right. thanks for your input on the my original question. guess i'm not as lost as i thought. thanks.
  21. J

    Physics HUP help

    p=0.05kg * 30 m/s = 1.5 kgm/s. 1.5 kgm/s * 0.1% =0.0015 kgm/s (delta x) > h/(2Delta p) where h is h bar ie) h/2pi delta x > 6.626*10^-34/ (4 *pi* 0.0015) delta x > 3.52*10^-32 like i said, i tried this method with another question, but i gave the kinetic energy and a 5% accuracy...
  22. J

    Physics HUP help

    honestly i haven't figured out where to start. i can get momentum by multiplying the mass and the speed. i wanted to multilpy that by 0.1% to get a delta p value and then solve for delta x. this is the method i used for other questions, and i did not get the right answer. also i am not...
  23. J

    Physics HUP help

    A ball of mass 50g moves with a speed of 30 m/s. If its speed is measured to an accuracy of 0.1%, what is the minimum uncertainty in its position? What does this answer indicate about the relevance of quantum mechanics to macroscopic objects? I am completely confused. My prof just gave us...
  24. J

    Parametric equations for particle motion

    Describe the motion of the particle with position (x,y) as t varies over the given interval. x=2+cost y=3+sint where t is greater than or equal to 0 and less than or equal to 2 pi i've tried to eliminate t and came up with y=3+sin(arccos(x-2)) i don't know if...
  25. J

    Power series representations

    the problem is that i only know how to get the power series rep for the arctan x part of the integral. i can't figure out how to get the representation for the whole thing. once i have that sorted out, the radius of convergence should be simple. any advice on how to solve the rest of the...
  26. J

    Power series

    that is the integral, thanks, but i am not sure what to do after pulling it apart into two integrals. quite honestly, i am puzzled by this whole topic. any advice?
  27. J

    Power series

    Evaluate the indefinite integral as a power series and find radius of convergence. (i don't know how to type the integral and summations signs, sorry) (integral sign) (x-tan^-1x)/x^3 dx. ( if you write this out it makes more sense) i was able to find the power series of tan^-1x =...
  28. J

    Power series representations

    Evaluate the indefinite integral as a power series and find radius of convergence. (i don't know how to type the integral and summations signs, sorry) (integral sign) (x-tan^-1x)/x^3 dx. ( if you write this out it makes more sense) i was able to find the power series of tan^-1x =...
  29. J

    Leslie Cube (still)

    thanks for your input on this. glad to here i did it correctly, and of course i converted to kelvin, thanks for the heads up though
  30. J

    Leslie Cube (still)

    sorry, this was my question from yesturday, and now my assignment is due tomorrow. anyone have any help for me? A Leslie cube has a surface temp of 97C. One of its four side faces has an area of 100 cm^2 and is painted black. Calculate: a) the wavelength at which the spectral intensity...
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