The Quantum Mechanic

Neat video of dolphins playing with bubble rings.

This might be a first — the appearance of (which is clearly supposed to be) Thevenin and Norton equivalents in a mainstream comic strip.

Take a look.

He’s even right. A circuit of sources and resistors with only two external terminals can be collapsed down down to two forms, all three of which will yield identical results when you take measurements from those terminals.

The key measurements are the open-circuit voltage (V_oc) across the terminals and the short-circuit current (I_sc) through the terminals. From those you calculate the Thevenin resistance R_T = V_oc/I_sc.

The Thevenin form is an ideal voltage source of V_oc in series with R_T with the external terminals being connected to the “free” end of R_T and the “free” end of the voltage source. The Norton form is an ideal current source of I_sc in parallel with R_T and the external terminals being connected across R_T.

So indeed, even when nothing is connected to the terminals, the Norton form will be pumping current through the resistor while the Thevenin form will be quiescent. So Alex is quite right that the Norton form will be warmer.

Best. Explainer. Ever.

Here’s something pretty cool…

Put a particle into an excited state. Then in a time very short compared to the lifetime of the excited state (i.e. so the probability of having decayed back to the ground state is very, very low) check to see if the particle is still in the excited state. This will collapse the wavefunction and (almost always, because you picked the timing that way) guarantee the particle is in the excited state. Rinse, lather, repeat, and you can keep the particle in the excited state indefinitely.

But what’s really cool is that you don’t have to do an active test (i.e. see if the particle is in the excited state) — a passive test works just as well. For example, you can send in a photon that can only be absorbed if the particle is in the ground state.

So you can basically keep the particle in the excited state by doing almost literally nothing — after all, in theory you could use photons that you were planning to use for something else. And since almost none of them will ever be absorbed, you can still use the photons for whatever else you were doing, but with the side-effect of keeping the particle excited.

Pretty neat.

I made the mistake of listening to NPR today, and they were talking about the high winds plaguing Colorado today. After talking about the “hurricane-force winds” hitting CO (which turn out to actually be 30mph with gusts to 90), the reporterette doing the piece puts on her over-dramatic voice and comes out with this gem:

Differences in air pressure are causing these winds.

As opposed to what, phlogiston currents?

I was doing some googling on trichinosis and discovered that according to FDA regulations, the larvae are killed instantly at 144F.

So despite what people have been taught, there’s no need to cook pork to the consistency of shoe leather.

Cribbed from Volokh, I know, but you have got to see this illusion!

StormTrack has a very nice explanation of hurricane eyewall replacement cycles. These cycles are one of the reasons why a storm can quickly go from Cat 5 to Cat 3 to Cat 5 again.

On the topic of hurricanes, I’d like to see a calculation of the thermodynamic efficiency of the things. Of course, one would first have to come up with suitable definitions of input and output.

I’d also love to hear about good books on the physics of hurricanes. Not at the level of a meteorology major, but not for the masses, either. Actually, recommendations on a Meteorology 101 book would be appreciated, too — the kind of book that a college student who is going to major in meteorology would buy for his first class in the major.

The list is out.