OK, more than seven. Ferrite rings (aka cores) are used as inductive loads in circuits, among other things. Any alternating current in a wire creates a magnetic field. By looping the wire through the ring a few times, you will create a changing magnetic field inside, which will produce eddy currents. These currents create fields which oppose the induced changes (this is Lenz’s law). From the circuit’s point of view (I hope it will excuse me anthropomorphizing it; I know circuits dislike that) this is an inductive load, so the alternating current sees a higher impedance than the DC, and this knocks down any high-frequency noise you might have and reduces what you write onto the components being powered.
Archive for June, 2011
Pick your isotopes from the Chart of the Nuclides. The program plays the energy level decay cascade as a series of notes that sound (to me) like a xylophone/marimba. You can change volume, pitch and tempo of each, as well as the waveform played — square and triangle waves sound more “techno” (I picked the isobaric combo of Ce, Xe and Cs, all -135). There’s also a visual of nuclei emitting the gammas. Interesting.
Alas, Peanutwitter has gone the way of the Dodo, if that’s a Dodo who got extincted by some copyright lawyers. I was on the edge as to whether it constituted fair use, but there is an argument to be made that it was, and this, being the blogohedron, someone has made it.
Not that this will cheer you up.
Charles Schulz’s Peanuts comics often conceal the existential despair of their world with a closing joke at the characters’ expense. With the last panel omitted, despair pervades all.
[T]he new alloy — Ni45Co5Mn40Sn10 — undergoes a reversible phase transformation, in which one type of solid turns into another type of solid when the temperature changes, according to a news release from the University of Minnesota. Specifically, the alloy goes from being non-magnetic to highly magnetized. The temperature only needs to be raised a small amount for this to happen.
But if it’s a phase transformation, it should be happening at a specific temperature. Once the material has heated up and you get your magnetic field, what then? The article and press release on which it was based don’t go into that.
During a small-scale demonstration in a University of Minnesota lab, the new material created by the researchers begins as a non-magnetic material, then suddenly becomes strongly magnetic when the temperature is raised a small amount. When this happens, the material absorbs heat and spontaneously produces electricity in a surrounding coil.
Faraday’s law tells us this should happen upon the creation of the magnetic field, but once it has happened — nada. You would need to cycle between states to maintain a changing field needed to continually produce electricity, so after heating you would need to then cool the substance.
The paper confirms this requirement
The design of the coil is to give a maximal component of E parallel to the wire, thereby driving a current. A potential difference across the coil of opposite polarity is obtained on the reverse phase transformation upon cooling.
So here “directly” doesn’t mean “directly” in the sense that you slap it on a car engine and produce electricity. You need a temperature gradient, just like always, and in this case, you need to bracket a specific temperature. Promising, but these headlines always seem to outnumber new products by a fair margin.
There was a story I heard when I was a student, (perhaps/likely apocryphal) way before youtube made it possible to record and share the examples so easily, of a professor doing this demonstration, wrecking-ball-to-nose, but letting a student give it a try, and the student gave the ball a small push. Broken face.
(See you next Wednesday would have been a gag that probably none of the students would have understood)
Carl Zimmer has a nice comment on the warts of science: It’s Science, but Not Necessarily Right
Scientists can certainly point with pride to many self-corrections, but science is not like an iPhone; it does not instantly auto-correct. As a series of controversies over the past few months have demonstrated, science fixes its mistakes more slowly, more fitfully and with more difficulty than Sagan’s words would suggest. Science runs forward better than it does backward.
One thing Carl doesn’t get into is that replication isn’t the only way to test results of an experiment. Since repeating an experiment is unlikely to result in publication, what is more likely is for a researcher to change the experiment or at least the emphasis of the experiment rather than simple replication or refutation. Success will depend on the initial discovery being true, but the results will still be novel and publishable. However, that really only works if the original experiment was correct — if the investigation doesn’t pan out, you are still faced with the problem of trying to publish something that is not deemed “interesting” by the journals (another issue raised in the article).
There is a link to several ideas to put people back to work, but the focus is on painting rooftops white to save utility costs, and idea that was popularized by Steven Chu, the Secretary of Energy.
There’s a claim raised in the comments:
AC costs less than heating
Obviously the total amount you spend on heating and cooling will depend on the climate where you live, but what if we quantify this? A degree of heating vs a degree of cooling? Then it becomes easy to make a comparison to see how compelling rooftop painting might be — if you have comparable degree-days of each, then whichever is cheaper tells you which way to go.
The basic argument is a simple application of thermodynamics. All nonreversible thermodynamic processes (which include your heating and air conditioning) reject heat. In the case of heating, though, the goal is to produce the heat, which means you can build heaters which are basically 100% effective. Cooling, however, has to reject heat, and becomes less efficient as it becomes hotter outside. Cooling efficiency is necessarily less than 100%, which means cooling an arbitrary mass by a degree costs you more in energy than heating it does.
Then there is an economic analysis — are you using the same energy source for cooling and heating (say, gas heating vs electricity for cooling) and are those energy sources costing you the same, and how much heating and cooling do you do? If you live in a dry area you can use a swamp cooler, which is probably relatively cheap. But make no mistake — the energy to cool by a degree is greater than the energy to heat by a degree.