Recent content by indie452

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    Molar heat capacity in metals and ionic solids

    I am doing my revision and noticed that metals all have a molar heat capacity ~25 J/mol/K = 3R. Ionic solids such as NaCl and CaF2 however have different molar heat capacities. (~51 and 72 respectively) Why is this? there is no explination that my lecturer gave and I can't find it online but...
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    How to Estimate Background Levels in Photon Count Data?

    Homework Statement I have been given some data, which is 20 successive 500second bins containing raw photon counts.(ie signal+data) The xray source is known to show flaring and from optical properties one suspects that it may show eclipses lasting ~1000sec. I need to estimate the...
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    Showing that a model is not a good fit

    thanks for replying so this is what i have got from your response: so if my area calculated is the prob of getting more than the chi squared (216) is 0.0345, then this means that at a 5% significance level it is unlikely that we will get a result of more than 216. but I am not quite sure...
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    Showing that a model is not a good fit

    ok so i have some data (d) of star counts (N=181), and a model (m = b-Fo where b=5 and Fo-constant flux) I have found the chi squared value = 216 I know that the number of degrees of freedom here is N-parameters = 181-1 = 180 my question is: "show that the model is not a good fit to the...
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    Mode of a probability distribution

    Homework Statement I have a luminosity prob distribution that i want to plot and find the expectation value and mode for. Homework Equations p(L)dL = A \frac{L}{i}^aexp(-\frac{L}{i}) \frac{dL}{i} A=const a= -0.7 i= 1.4e10 solar luminosity units lower limit = 1e9 solar luminosity...
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    What is meant by density in units of critical density?

    what is meant by density, such as the baryonic matter density in cosmology, in "units of the critical density"? its mentioned in a question i need to do but i don't really know what it means.
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    Taylor Expansion for (a(1+z)^3 + b)^-1/2 around z=0 to First Order

    Homework Statement I have the function (a(1+z)3 + b)-1/2 and i need to taylor expand it around z=0 to the first order, a and b are constants, there sum is equal to one. I have the answer: 1 - (1+q)z where q = a/2 - b This is in my physics book but it does not explain the...
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    Calculating Particle Spacing in a Lattice Using Fourier Transform

    Homework Statement Okay so i am applying a FT to an image of particles that are forming a lattice, and i need to find the average distance between the particles because its not a perfect lattice, I am getting an airy pattern and i believe that the distance to the first ring is the average...
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    Positron-electron collision can someone check my answer?

    wait is it just zero?...thats what i got from doing some rearrangement (too much to write out)
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    Positron-electron collision can someone check my answer?

    ok so on the left the Ecm is 1000GeV, is pcm2c2 = Ecm2 - m2c4 ...wait i don't think that helps... my lecturer didnt really go over how to get the momentum. the only thing he metioned ws the 4momentum but i don't think that is what i use here
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    Positron-electron collision can someone check my answer?

    well i set it to m2c4 cause this is the invariant mass and so i can find this in the lab frame and it will be the same in the cm frame. when i found the relation for this i went to the cm frame to use its Ecm to find the energy i need for the beam. now while writing this i think i should...
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    Positron-electron collision can someone check my answer?

    as in that i should have put (2m)2c4 on the left hand side?
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    Positron-electron collision can someone check my answer?

    (E+mc2) is the sum of the energies of the 2 particles. the e- is stationary so i thought that its energy is just mc2 in the lab frame p2c2 i didnt put a p(e+) +p(e-) because the momentum of e- is zero so its just the mom. of the e+
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    Positron-electron collision can someone check my answer?

    ok so i tried this instead mass of e+ and e- => m2c4 = (E+mc2)2 - p2c2 = E2 - p2c2 + 2Emc2 + m2c4 = 2Emc2 + 2m2c4 and as mc2<<E m2c4 = 2Emc2 now this is where I'm abit unsure: can i say: m2 = (1000GeV)2? cause this would give (1000GeV)2 = 2E(0.51MeV) so E = 1.96x1018eV
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    Positron-electron collision can someone check my answer?

    where is it that I've gone wrong? what would you suggest to try and get the right answer?
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