Recent content by jewbinson

  1. J

    Heating water by dropping it from a high height.

    Yes but as soon as the water ends up in the tank, it moves the tank and then the Earth. I imagine most of the energy from the KE of the water gets transferred into the KE of the Earth. Think about it. If the Earth were a ball of 10cm radius then most of the KE of the water would transfer into KE...
  2. J

    EPE at a point due to two point charges

    With regards to this setup of two point charges, I was thinking the other day (assuming both charges are the same magnitude and opposite sign...) What is the equation of motion? If we write Coulomb's Force Law then the equation seems hard to solve. Can we use energy/ work done equations to solve...
  3. J

    Quantum states of matter

    You mean assume the radius of the universe is 1 googolplex metres, or 1 googolplex quantum particles?
  4. J

    Heating water by dropping it from a high height.

    Good point on surface tension. I guess that's as deep as we need to go for the purposes of answering OP's question.
  5. J

    Heating water by dropping it from a high height.

    This is just common sense (well, to me anyway). Assuming all the energy gets transferred into heating the water and none of that heat gets lost, then yes, all the kinetic energy heats up the water. But this never happens in reality due to the nature of materials and their properties. In real...
  6. J

    Electric field of a charged disc

    I see. Considering (a/z)<<1 or instead considering (a/z)^2<<1 leads to the same result (no information is lost w.r.t. the Binomial expansion approximation). But in both cases x = (a/z)^2
  7. J

    Electric field of a charged disc

    I'm not sure I get that at all. Are you sure you're not considering (a/z)^2 and therefore (a/z)^4 << 1 and similar for higher order terms? Because then the Binomial expansion formula would seem to work. I'm not used to using it with the exponent non-integer. What I said in my last post is...
  8. J

    Electric field of a charged disc

    Right. At first I tried taylor series at x=0 but didn't try it at x = infinity. I guess I hadn't come across using expansion about infinity in physics yet... only complex analysis. Maybe there is something simple I am missing but why do you automatically look for expansion about infinity...
  9. J

    Gravity and water slides

    On twists/turns in the slide, do lighter/smaller people go higher up on the bend than heavier/larger people? (in general)
  10. J

    Electric field of a charged disc

    ... with constant charge density σ = Q/((pi)a^2) The Electric field is, after some calculation, is given by E_p below: z is the z-axis, and a is the radius of the disc. Now for the questions at the bottom of the page, here are my thoughts: σ is independent of a because as a->2a, Q->4Q, and...
  11. J

    My bra-ket calcs seem to be going wrong - help!

    I agree with what The Duck said. I will take this a bit further for your curiosity's sake. Define the Parity operator P by P|x> = |-x>. The eigenvalues of P can be either 1 or -1 (try and prove this or tell me if you can't. Hint for proof: consider P^2 and it's eigenvalues). These are the...
  12. J

    Meaning of Quantum Spin

    It should be noted that since an electron is a fundamental particle, it has no internal structure, and so the spin of an electron does not have any relation to it's motion internally (i.e. the electron does not spin round like the Earth spins round on it's axis). Spin is an intrinsic property...
  13. J

    Quantum Mechanics to a Newcomer

    Edit: and if not, you should opt out and go for the engineering/beginners one one
  14. J

    Quantum Mechanics to a Newcomer

    You should tell your lecturer the situation you're in and ask him if you'll survive (the course) if you carry on. He will know the answer better than anybody.
  15. J

    Radial wave function in H atom

    "Mathematical methods for physics and engineering" has a chapter dedicated to these functions. I would also recommend this book as the essential maths reference book to anyone taking a degree in a related area (maths, physics, engineering etc). Edit: make sure you get the latest edition (if...