Recent content by Jess

  1. J

    US Universities for Postgraduate Studies in Astrophysics

    Hi A couple of years ago I was in your shoes, wanting to do a PhD and also study in the states. I ended up staying in the UK because the cost of studying in the states was prohibitive, and also I'd already done a Masters course, so the thought of spending 2 years redoing all the stuff I'd...
  2. J

    Other planetary systems

    No-one has successfully imaged an extrasolar planet yet, but we're getting closer! http://www.roe.ac.uk/atc/news/pressrelease/20031201/index.html [Broken] Jess
  3. J

    Relativity Paradox: Explaining A Ship Moving at 198% Light Speed

    The two-accelerated-particle case has a higher total energy (invariant mass/energy + kinetic energy) than the one-accelerated particle case, so if the two particles were to annihilate on contact, for example, the EM radiation produce in the first case would have higher energy (higher frequency)...
  4. J

    Are There Any Isolated Black Holes? Name a Few Here

    There is a radio source at Sgr A* though - thought to be very low level activity due to heated matter orbiting the BH. Jess
  5. J

    Is there a blackhole in the centre of EVERY galaxy?

    It looks very much as if every galaxy with a central bulge has a black hole. But bulgeless galaxies such as M33 do not appear to have sufficient central stellar velocity dispersions to contain central supermassive black holes. Until enough nearby galaxies have been surveyed, however, that'll...
  6. J

    Only four fundamental forces in the universe?

    The Higgs boson is required to explain why the particles that mediate the weak nuclear force - the W and Z - are so massive. The extraordinarily high masses of these particles are mathematically inconsistent with the Standard model, so particle physicists postulated the existence of another...
  7. J

    Heat problem and unreasonable heat rates

    I found values ranging from 385 W /m K to 400 W/ m K. So I suspect this is the difference between mks and cgs systems of units. I don't get 68W, even when I use cgs units - unless I use cm for the thickness and m for the diameter, interestingly. Jess
  8. J

    Heat problem and unreasonable heat rates

    Dimensionally at least, 0.5MW is correct Jess
  9. J

    Heat problem and unreasonable heat rates

    The 0.5MW is only the heat conduction rate - it says nothing about how much of that heat is actually transferred to the water. There'll be losses and all sorts. I suspect that these points (plus some others that haven't occurred to me) will make up the second part of part (b)... Jess
  10. J

    Thermal resistance, can i do this?

    Try http://personal.cityu.edu.hk/~bsapplec/newpage218.htm It seems to answer some bits of your question. From what I've found, it looks like you can combine thermal resistances in series the way you've done it. Jess
  11. J

    Heat problem and unreasonable heat rates

    Sorry to point out the obvious, but this isn't an electrical conductivity question, so that comparison just doesn't stand up. The thing is, in this question the temperature gradient is high - 20,000 K/m, which is what gives the high rate of thermal conduction. Jess
  12. J

    Heat problem and unreasonable heat rates

    0.5 MW isn't that big - and don't forget that the thermal conductivity of copper is unusually high. As far as I can tell from a quick dimensional analysis the units are all okay, so the answer should be correct. Jess
  13. J

    Heat problem and unreasonable heat rates

    For a start, you've got the diameter in centimetres but the thickness in metres... Jess
  14. J

    Good read for basic background info

    Or Shu's 'The Physical Universe'. Some bits are a bit out of date these days, but it's still excellent for all the basic stuff. Jess
  15. J

    Gas Cylinder Discharge Time: Solving for V2 Vent

    I assume that the tank empties because the gas inside is at greater than atmospheric pressure. When the valves are opened the tank pressure changes until the pressure in the tank is the same as the pressure outside the tank. This way it doesn't matter how the tank empties as long as the...
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