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  1. K

    Thermodynamics, two equal volumes of gas at STP mix, entropy change?

    As far as ive researched it is infact zero due to the fact that the molecules are indistinguishable from each other, the partition can just be reinserted and the thermodynamic state is the same so it hasnt changed in entropy.
  2. K

    Thermodynamics, two equal volumes of gas at STP mix, entropy change?

    but how do i go about proving entropy change is zero
  3. K

    Thermodynamics, two equal volumes of gas at STP mix, entropy change?

    Homework Statement Calculate entropy change if two equal volumes of gas (1 cm3) at standard temperature and pressure are separated from each other by a partition which is removed to create twice the volume at standard temperature and pressure Homework Equations dS = k.N. dV/V + C/T dT...
  4. K

    Characterize a co2 TEA class 4 laser

    No1 want to add anything?
  5. K

    Characterize a co2 TEA class 4 laser

    Homework Statement Im working on a lab experiment in my undergraduate physics degree requiring the use of a class 4 laser, i need to characterize this in terms of its power, coherence, pulse duration, wavelength and irradiance. This is a pulsed laser with rough parameters of 1-2J pulse energy...
  6. K

    Easy Question, Sunspots Astronomy Umbra and Penumbral sunspot areas

    Thats a good link but doesnt explain the significance of the areas of the umbra and penumbra areas shamefully....
  7. K

    Easy Question, Sunspots Astronomy Umbra and Penumbral sunspot areas

    Can anyone explain the significance of the umbra and penumbra areas?
  8. K

    Easy Question, Sunspots Astronomy Umbra and Penumbral sunspot areas

    Ive jsut spoken to a friend that used photoshop and the lasso tool to outline the areas then using one of the options it will give a pixel count. i can understand how this will give me the area, and thus the ratio, but not how i could quantify any errors in this calculation.. Thanks for the reply
  9. K

    Easy Question, Sunspots Astronomy Umbra and Penumbral sunspot areas

    Didnt know if this is the write palce to put this, but im stuck on this assingment and i think it must have an easy solution so if someone could point me in the right direction then it would be much appreciated. Homework Statement Using an appropriate software package, quantify the...
  10. K

    Calculating values of electric and amgnetic fields of laser beam

    Ok, didnt realise that equation, so using those values E = \sqrt{2S\mu c} ? Therefore E = 119959.9933 V m^-1 ? H = E/c\mu ? Therefore H = 318.4160428 A m^-1 ? I tried to confirm the equations using dimensional analysis: E = V m^-1 mu= kg·m·s−2·A−2 C = m S^-1 S = J s^-1 m^-2 I cant get that...
  11. K

    Calculating values of electric and amgnetic fields of laser beam

    for fear of asking the obvious, S being?
  12. K

    Calculating values of electric and amgnetic fields of laser beam

    Sorry, i mean to say i dont know how i would get H B or E. i can see easily how with any of the variables allows the other for calculation but im at a loss to get any.
  13. K

    Calculating values of electric and amgnetic fields of laser beam

    Homework Statement A continuous wave laser beam in free space carries a power of 15w and has a circular cross section with diameter 1mm. Calculate peak values of the oscillatory electric and magnetic fields Eo and Ho repectively. Homework Equations Eox = (\mu/\epsilon)^1/2 Hoy \pir^2...
  14. K

    Calculate capacitance to adjust current in ac circuit

    Homework Statement A Purely resistive resistive 100w, 110v lamp is to be supplied by an a.c. source of 230v r.m.s at 50Hz. what value of pure capacitance could be put in series to adjust the current flow to a suitable value? Homework Equations p=iv q=cv v=ir i know a number of other...
  15. K

    Extracting a square root

    hi, instead of squaring both sides, try multiplying them out as you know (x-7)^2 is the same as (x-7)(x-7) ..
  16. K

    Reversible adiabatic expansion of ideal gas, entropy change?

    i know \Delta S = \int_1^2 dQ/T + \int_2^3 dQ/T but dQ is zero for an adiabatic process isnt it? Khris
  17. K

    Reversible adiabatic expansion of ideal gas, entropy change?

    Homework Statement One mole of an ideal gas at 0 celcius is subjected to changes below, calculate the change in entropy of the gas: i) Gas is expanded reversibly and isothermally to twice its initial volume. DONE - 5.76 J/K ii)A similar expansion to i. is performed reversibly and...
  18. K

    Thermodynamics Entropy change of the universe

    im sorry about not including the full calculation, the integral becomes LnT, inbetween the limits it becomes Ln(303/277) multiplied by the specific heat capacity. So the heat flow into the can of beer is + 224, then the heat flow from the surroundings is negative -214, would i add these...
  19. K

    Thermodynamics Entropy change of the universe

    that equation gives change in entropy as the sum of how the energys changing as the temperature changes is it not? when integrated between the limits of the initial and final temperatures? Khris if i use the equation that change in entropy = heat flow / temperature...
  20. K

    Thermodynamics Entropy change of the universe

    ok so the loss from the surroundings is correct, but the value for tha can is incorrect i can see that. i know also the equation: but cant think how to use it.
  21. K

    Thermodynamics Entropy change of the universe

    Im trying to do an assingment for second year BSc, ive thrown alot of effort into quatum this semester so have fallen a little behind with thermodynamics so help is appreciated! Homework Statement Calculate the change in entrupy of the universe for the following processes A can of beer...
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