Recent content by ironhill

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    Newton's Cooling Law: q = h*a \Delta T

    Newton's law of cooling: If you put milk in your coffee then leave it for a minute it will be warmer than if you leave it for a minute then add milk.
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    How does classical fail in here

    Acceleration means changing velocity, a particle going in a circle has velocity that is changing (direction). Accelerating particles radiate. If you want to know why you really have to do the math, you can't prove anything arguing qualitatvely. It is a fact that accelerating particles...
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    Which interpretation best explains the classical limit?

    The question of how a large mass particle, like an ideal tennis ball, behaves is goverened adequetly by Ehrenfest's theorem. Spreading of a wavepacket is essentially nil (for a Gaussian wavepacket I think there's a factor (h/m)^2 can't remember offhand, it's in Merzbacher). If you want to talk...
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    Ideal conductor vs superconductor

    Of course, but since it's ideal we ignore residual resistivity from impurities and lattice distortions and so on. That is in fact how supercondctivity was discovered. Osanger wanted to see if the resistivity of a metal (mercury) would keep following that smooth curve all the way to 4K. The...
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    Which interpretation best explains the classical limit?

    Ehrenfest's theorem gives you back Newton's laws and the usual classical equations for momentum and energy and so on. These predict the motion of a tennis ball pretty well.
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    How does classical fail in here

    The argument relying on a moving proton is invalid, for one thing you can use the reduced mass and forget about it completely. Where does the energy come from? Potential energy due to the proton in the middle depends on 1/r, so does kinetic energy (equate centripetal force and coulomb...
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    Ideal conductor vs superconductor

    An 'ideal conductor' is a conductor where the resistivity drops away following Matthiessen's law all the way to 0K. The practical consequences of the Meissner effect? Well for one it means that the suerconducting state is a Thermodynamic state. The state of an ideal conductor depends on B and...
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    Klein-Gordon Approximation Question

    No need for Taylor expansions, just algebra, keep stuff of 1st order of smallness, expand the square; E^2 -> m^2 + 2m\epsilon 2EV -> 2mV V^2 -> 0 Stick that in and you get it.
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    Calculating the Number of Bounces for a Moving Ball

    Shooting Star got what I meant, motion in the horizontal and vertical directions carry on independantly of each other, which made me think you might be able to figure out the number of bounces after a given distance since you know the initial velocity in the horizontal direction and so u*t = x...
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    Calculating the Number of Bounces for a Moving Ball

    A ball rolls off a table with initial velocity u (say 1m/s). Every time it hits the ground its velocity is halved. Find how many times it has bounced when it has traveled a distance x (say 1m) from the table. I am almost sure that you can do this without knowing the height of the table but I...
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