Monthly Archives: December 2012

Narrowing the Gap

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Laser pulse makes insulator conduct like a metal

Silicon dioxide is an insulator with an energy bad gap of about 9 eV separating its valence and conduction bands. In contrast, the band gap in silicon is about 1.1 eV; this means that, in principle, a switch made from silicon dioxide could operate much faster than a conventional silicon switch. The problem, however, is that a silicon-dioxide switch would have to operate at very high electric fields, resulting in a destructive electrical breakdown.

One way round this problem is to apply a strong electric field for an extremely short time, so that breakdown does not occur. When the field is applied, some of the electron states in the valence band increase in energy while some states in the conduction band decrease. The upshot of this is a significant reduction in the amount of energy required to create a conduction electron and the material becomes an electrical conductor.

Misconception or Approximation?

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For the second time in the past month, Minute Physics is making a statement about what gets taught in introductory physics. It is consistent, but I still disagree. I have had too many interactions with people who want to discuss relativity (or quantum mechanics) and are either very confused or think its wrong, and this is exacerbated because they have no familiarity with classical physics.

I have no problem with telling students that what they are going to learn in introductory physics is an approximation, but the claim that presenting Newton’s gravitation equation is akin to telling students that the earth is flat is an exaggeration. If you go down that path, then what of all the other approximations that we make in physics? Speaking of a flat vs curved earth, do you really want to force students to solve trajectory problems on a curved surface rather than flat one? Is a frictionless surface a lie, or is it a convenient approximation to simplify a problem? And, on the topic of friction, should we really delve into the morass that is friction, rather than just say that it’s proportional to the normal force and try and get the big picture across?

I think the objections are wrong in a few different ways — One of the principles you learn in solving problems is how to ignore complications that do not affect the answer to the question. Also, learning physics through to relativity and other advanced topics takes years of study. Introductory classes carry with them the need to prune the information to fit, and convey the material that is most important to the students’ needs. Most of them don’t need to learn about relativity, which is why it’s not part of the introductory classes.

Don't Flatter Yourself, Otter. It Wasn't That Great.

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Physicists Bummed That Physics Is Pretty Much What They Expected

Great title (no, it’s not The Onion), but not much more than a lead into another story:

At CERN: Down in the Mouth in Paradise

Chalk up another success for the Standard Model. How … ummm … exciting?! Sure, if you’re over 60 and fondly recall the glory days of the 1960s and early ‘70s when the Standard Model became, well the Standard Model. Or if you’re an experimentalist who has dedicated the last 10-30 years to designing, building and operating the extraordinary Large Hadron Collider and Tevatron accelerators (where the discovery was made and confirmed respectively), or their monumental detectors — ATLAS and CMS, CDF and D0. Celebrate away. Drink champagne, toast your successes, wonder over Nobel and lesser (but more broadly shared) prizes. You’ve earned it. But what about the rest of us?

Good to the Last Drop

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The Ups and Downs of Making Elevators Go

Here is a typical problem: A passenger on the sixth floor wants to descend. The closest car is on the seventh floor, but it already has three riders and has made two stops. Is it the right choice to make that car stop again? That would be the best result for the sixth-floor passenger, but it would make the other people’s rides longer.

For Ms. Christy, these are mathematical problems with no one optimum solution. In the real world, there are so many parameters and combinations that everything changes as soon as the next rider presses a button. In a building with six elevators and 10 people trying to move between floors, there are over 60 million possible combinations—too many, she says, for the elevator’s computer to process in split seconds.

“We are constantly seeking the magic balance,” says the Wellesley math major. “Sometimes what is good for the individual person isn’t good for the rest.”

Rube-y Goldberg Tuesday, Hanukkah Edition

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[A] Rube Goldberg machine that lights the Chanukah menorah. Hanukkah is the holiday of miracles and here is another one.

(Personally I think a consistent spelling of Chanukah/Hanukkah would also be a miracle.)

I’m a little disappointed in the camera work — many shots are too tight and quick, IMO — you don’t get a feel for the inter-connectedness of the device. And the use of a robotic arm at the end isn’t kosher (I’m more of an orthodox Goldbergist.); I thinks it’s more accurate to say that the R-G device starts the robotic arm, which then lights the menorah.

Hello, Polly

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Goodbye, fluorescent light bulbs: New lighting technology won’t flicker, shatter or burn out

The device is made of three layers of moldable white-emitting polymer blended with a small amount of nanomaterials that glow when stimulated to create bright and perfectly white light similar to the sunlight human eyes prefer. However, it can be made in any color and any shape – from 2×4-foot sheets to replace office lighting to a bulb with Edison sockets to fit household lamps and light fixtures. This new lighting solution is at least twice as efficient as compact fluorescent (CFL) bulbs and on par with LEDs, but these bulbs won’t shatter and contaminate a home like CFLs or emit a bluish light like LED counterparts.

Still waiting for the other shoe to drop — new technology doesn’t always pan out, though this seems closer to production than most. No mention of how the price will compare to existing products; despite the generally lower total cost of ownership of CFL and LED bulbs, some are put off by the price of the bulb. Also, FIPEL? I think that will get reworked for public consumption.