Built on Facts: Bose-Einstein Condensates, pt. 1
Part 2 and part 3
Category Archives: Physics
Fun with Magnets
I’ve done several of these, including a version of the homopolar motor. The eddy current damping is fun, too — you can make nonmagnetic metals react to magnets by inducing current flow in them. Lenz’s law.
More Ideal Gas Demonstrations
A mole of an ideal gas takes up 22.4 L at STP. Burning a hydrocarbon makes lots of H20 and CO2; the latter is 1-for-1 with the oxygen in the air, but the water is 2-for-1. Plus the heating, which causes the expansion or pressure increase. But I’d like to see what happens after a little time has elapsed and the gases cool off and the water condenses. I suspect you need to hook the tire up to a compressor really soon — this is a trick to seat the tire on the rim.
No Grace Under Pressure
Atmospheric pressure is about 10 N/cm^2, but there are a whole lot of square centimeters on that tanker — the more familiar unit is N/m^2 (Pascals), where 1 atmosphere is 101325 Pa (or possibly even more familiar 14.7 psi).
Various sites showing this have claims about this happening after the tanker had been heated (from steam cleaning), and all the valves shut while it was still hot. One claims frozen (perhaps they mean liquid?) nitrogen being added. Plausible? Heating the tanker to 373K and then letting it cool to ambient should drop the pressure by 0.20 atmospheres. A tanker that’s 2 meters in radius and 10 m long has a surface area of 125.6 m^2, for a total force of 12.7 MegaNewtons. 20% of that is a lot. I don’t think the liquid nitrogen is strictly necessary, but would add to the effect.
The heat of vaporization of liquid nitrogen is 5.56 kJ/mol and its specific heat capacity of the gas is 29 J/mol-K. The volume of 125.6 m^3 means 5600 moles of an ideal gas, requiring 160 kJ/K to cool it down. Each liter of liquid nitrogen (29 moles) takes about 160 kJ to boil off, and then another .84 kJ per degree as the gas heats up from 77K. So ten liters of liquid nitrogen dumped into it will cool it about 20-25 degrees, depending on the starting point of the tanker. So that won’t hurt, but what’s probably more important is that the tanker was built to withstand some pressure difference and we see the catastrophic failure when its critical pressure difference is exceeded. Unlike the kind of test you can easily do with a can where you boil some water inside, seal it and watch it crumple as it cools, because it wasn’t designed to withstand and significant pressure difference.
Beans on Toast
Many unaware of alcohol calories
Pint of cider = Beans on toast = 200 Calories
“British cuisine” is an oxymoron
Laser With Controllable Polarization
To achieve the results, the researchers sculpted a metallic structure, dubbed a plasmonic polarizer directly on the facet of a quantum cascade (QC) laser. The QC laser emitted at a wavelength of ten microns (in the invisible part of the spectrum known as the mid-infrared where the atmosphere is transparent). The team was able to control the state of polarization by generating both linearly polarized light along an arbitrary direction and circularly polarized light.
The Groaning Grid
I remember when I was discussing a story about fast-charging batteries with someone that there was the conjecture that this was the hurdle to getting electric cars on the road. And I realized it wasn’t — heat dissipation issues aside (charging a cell-phone battery is one thing, but trying to scale that up is quite another) — the real issue is how much energy you need and how quickly you can deliver it. Grid capacity.
Electric cars will travel a few km per kWh of energy, so a 350 km range takes about 100 kWh, or 3.6 x 10^8 Joules. The good news is that this is more efficient than gasoline, which lets you go about 1 km per kWh. A gallon of gasoline has a little over 10^8 Joules stored in it, so 31 mpg is about 50 km/gal, and that makes an electric car with the above specs about twice as efficient. But if I can pump a gallon of gas in ten seconds, that means my energy transfer rate is 10 MW. That’s about 3 orders of magnitude higher than standard electricity delivery.
It’s pretty clear that any electric solution in the near future is going to involve shorter-range vehicles, be they pure electric or plug-in hybrid, which you could recharge overnight.
Challenges to grow with electric cars’ sales: Aging grid needs to handle more power
When a Chevrolet Volt is plugged into a 240-volt outlet, it will use about 3.3 kilowatts of power, or about the same amount of power as a dishwasher or air conditioner.
Most people are already familiar with what can happen when thousands of air conditioners are plugged in and running at the same time during the summer: brownouts.
“The last thing we would want is for everyone to come home … and plug them in at 5 or 6 o’clock on a hot, muggy summer afternoon … when we are at our peak,” DTE Energy Chairman Anthony Earley Jr. told the Free Press in an interview recently.
US residential consumption is about 30 kWh of electricity every day; houses probably more and apartments less. Regardless, 3.3 kW for 8 hours = 26.4 kWh, which is a significant bump.
You'll Shoot Your Eye Out
New laser pointer. 20 mW, $20. Elicited some “gotta get one” responses, as well as “That’s bright!” (It is, too)
It’s supposed to say “Laser” (3 second exposure on the camera)
Laser writing is hard. No mechanical feedback, no visual feedback.
Two For One
One of the things we’re investigating is pulsed laser systems, because they’re fun, but (especially for funding purposes) also because they are the basis of optical frequency combs (as I’ve mentioned). And things are pulsing along. One of the things that was noticed was that light from the pulsed system, running at 1560 nm, was showing up on a Silicon CCD camera. The Silicon response peaks at 900 nm and drops pretty sharply, petering out at 1100-1200 nm. There’s no way it should respond to a 1560 nm photon.
And it isn’t. It’s responding to pairs of 1560 nm photons. This is a pulsed system, so you have high peak power making it a lot easier to see nonlinear responses like two-photon transitions, because they scale as the square of the intensity. (more photons incident per unit time means a better chance to have two interacting at once, Having n photons means that if you look at any photon, the chance of another photon being around is n(n-1)) Two photons have enough energy for the interaction, since that’s the same as having a 780 nm photon, which is well above the “to be detected you must be this tall” energy cutoff
Here are two images. The square is a beamsplitter cube, and the white blob is the light. The top image is the pulsed laser, and the bottom one is a CW beam, both with around 10 mW average power.
The pulsed laser is saturating the heck out of the CCD, so the spot is really a lot brighter than from the CW beam, though we can’t say for sure based on this quick look. Even though the average power is about the same, though, the pulsed laser is repeating at about 10 MHz, and the pulses are less than a picosecond, so all of the light is being delivered in less than 10-5 of the time, so the peaks have powers measure in kW.
Worthless? Bah!
physics and physicists: “I’ll Never Use The Skills I Learned In Physics”
zapperz attacks this in a couple of ways, such as the idea that you (can) learn critical thinking skills
The “skills” that one learn out of a physics/science course goes BEYOND physics. It is a skill of thinking things through and systematically. It is the skill in knowing what KIND of evidence is required for something to be considered to be VALID. This is highly important no matter what you do. How do you know that something somebody utters on TV is valid? Most of the time, people are persuaded not based on valid evidence, but based on personality of the presenter and all the bells and whistles. Apply this to the world of politics, where phrases fly off into the air as if they are facts, or as if simply by saying it, it is true. The same can be said with regards to the battle between evolution and creationism. The inability of some members of the public to actually think through something THIS obvious clearly shows that the skill of analytical thinking isn’t there!
That and the other points are certainly important, but I’ll go a step or two lower and look at some actual physics applications. I don’t know precisely what is taught in Physics 140: How Things Work, but I’d guess a few basics involved would let you figure out that the truth about turning the heat down during the day if nobody’s home. “Conventional wisdom” says that it takes more energy to heat the house back up, but the actual physics confirms the conventional wisdom to be wrong. Or a simple analysis to verify that buying a long-life CFL will save you money over incandescent bulbs once you figure out actual energy use, despite the cost-per-bulb being higher. E = Pt is simple physics, but physics nonetheless.
A word of advice for Ms. McMillan: if someone asks you to invest in a device that creates energy, for which you will be able to charge money and make a profit, it may appear to be a sound investment from a financial perspective. But the physics you so casually dismiss guarantees that it is not.
(on a personal note, I’ve found that most of basic finance is pretty easy if you can do physics. Problems in financial literacy and science literacy do share a common problem: math literacy)