I always get a warm, fuzzy feeling when Google recognizes physicists in their Google doodle.
Today is Hans Christian Oersted’s birthday, and this famous physicist has been shown the love:
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Danish natural philosopher Oersted was one of the first physicists to link electricity and magnetism. His work paved the way for James Clerk Maxwell’s revolutionary four equations that perfectly mathematically-modeled electromagnetism.
Congratulations to Bill Ruhsam for the first episode of Talking Traffic, a podcast explaining issues in traffic engineering to the vehicle-driving public. Full disclosure, of course: Bill is a good friend of mine from college. That doesn’t mean, however, that the podcast isn’t anything but top notch. Go have a listen!
In the first episode of Talking Traffic (listen here!) Bill elucidates for us the difference between coordinated, synchronized, and actuated traffic signals. Actuated signals use metal loops embedded in the pavement as a switch to inform the traffic signal’s computer that a vehicle is present. But how do these loops work?
For the longest time, the naïve little physicist in me thought that somehow these devices were actually huge scales that weigh your vehicle — any significant weight would be enough to trip the signal and get you that green light. Silly me!
Using massive scales would be impractical. Have you ever seen a road construction worker using a jackhammer to chip away at pavement? The area comprised by the metal loops in the road is probably about eight feet by eight feet, so a jackhammer operator would have to be working on the road for weeks just to clear enough pavement to put in a device. Such a scale would be expensive, hard to maintain and install, and barely be worth the effort.
Only after I started studying physics did I realize how those loops could really work. Using the natural phenomena of electricity and magnetism, metal loops can determine the presence of objects near them without any contact at all. This is called electromagnetic induction.
It may not be obvious that electricity and magnetism are related. When electric charges move, they produce an electric current. When an electric current travels in a long straight wire, it produces a magnetic field in concentric circles around the wire. If you coil up the wire, the fields add up in such a way that it’s as if there’s a large magnetic field that points in the same direction as the object you’re coiling the wire around. The picture on this page supplied by the Collaboration for Nondestructive Testing says in an elegant picture that which I have trouble saying in words.
Perhaps in science class you made an elementary electromagnet by wrapping wire around a nail, and then connecting the wire to a battery? You didn’t? Try it now! You can pick up paper clips! The more turns of wire (or the higher the voltage of the battery), the more paper clips you can pick up. This is the exact same phenomenon.
Let’s extend this to the traffic loop. If we provide a small current, a magnetic field will be produced pointing upwards out of the surface of the road (or inwards, down to the ground, depending on the direction) of the current in the wire. Energy is stored in that field, which (essentially) serves to resist any change to its state. The quantity that defines the amount of resistance to change is called the inductance.
It’s possible to measure the inductance of a loop. Cars are made of conducting materials. When a car enters the area over the loop, the conducting material enters a magnetic field. Small loops of current are created. These “eddy currents” serve to make their own field which tries to resist the changing field. That is, an opposing magnetic field is produced.
The opposing magnetic field manifests itself by changing the inductance of the loop. A computer, probably in one of those unmarked boxes at the corners of intersections, constantly polls the loop for its inductance value. Once an inductance outside the normal range is measured, the computer handles the traffic signals accordingly.
The concept of electromagnetic induction is very tricky to grasp. In fact, induction is the key concept in electrical transformers, power generators, magnetic-levitation trains, and some braking mechanisms. Without a firm grasp of induction, much of our modern electrical infrastructure wouldn’t exist.
Thanks for driving by.
I turned thirty-two a couple of weeks ago. Seeing as this was a major milestone (I’ve turned 0x20!), I figured it was time to get into better shape. I’ve had some chronic back pain the last few months, and when I was undergoing physical therapy the therapists recommended that walking and running would be a very good way to strengthen my back muscles.
The past few days I’ve really gotten into my running. I go to a local park at which during the day music from a local radio station is played over the loudspeaker. Since I’m probably one of the few people in the country remaining that does not have an iPod or other MP3 player for exercising, the music is at least something to take my mind off of the almost-pleasant torture that is running in a circle for a half-hour.
In particular, this radio station prides itself on providing a “safe” listening environment for mothers and their children. There’s nothing wrong with that. The result is that most of the ads are intended towards women. Three times I’ve heard an ad now for a local shopping center chain, Hannaford. The ad describes Hannaford’s efforts to remain environmentally-friendly as they do business.
I don’t have a problem with this. Most companies don’t make much of an effort to be green because there’s no financial incentive. If Hannaford wants to make this a selling point, good for them. As people increasingly see a company’s environmental policy as a reason to go there, there will be an economic incentive for companies to think about the environment as they do business.
Two things struck me as odd, though. First, as the chipper woman in the ad is proud to mention, “Hannaford recycles over one hundred million pounds of waste per year! That’s fifty thousand tons, more than the Titanic!” Fair enough, that’s all correct. I applaud Hannaford’s efforts, but wouldn’t it be more valuable for Hannaford to not waste anything at all? The old adage goes that reuse is better than recycling. It seems a little silly to me to be advertising that you waste a cruise-ship-size mass of junk every year, but whatever. Then again, I also don’t have anything to which to compare that number. Other local chains don’t readily publish their waste amounts, so for all I know the others waste ten times that amount.
The second thing was just plain weird. “By using environmentally friendly lighting, Hannaford saves 24,000,000 kilowatt-hours per year. Those 24,000,000 kilo-… umm, jiggers, *confused pause*, …is enough energy to power two thousand homes for a year!”
I would have loved to be in the ad company meeting where this script was pitched. What good does it do anyone to have the actor fake stupidity, especially when the real information has already been stated?
In the words of H. L. Mencken, “No one ever went broke underestimating the stupidity of the American public.” This may be true, and perhaps it is this guiding principle that Hannaford’s advertising firm lives by.
At best, this ad passively laughs at the science-illiteracy which pervades the public consciousness. At worst, the ad tells its listeners that science is just something for “those eggheads” to do. These small and arguably meaningless words in its monologue tells these stay-at-home parents, mostly moms, that they have no hope of understanding energy or environmental concerns. The messages then being sent from parent to child are that “science is too hard; you won’t understand!” Science is hard, but by making kids disqualify themselves from science from the beginning, they don’t have a fighting chance.
Rather than use this as a teaching moment, the ad company (and Hannaford by extension) continues to propagate the idea that science is for smart men, not everyone. Certainly, science as a career is usually pursued by smart men and women, but science literacy is important for every single citizen of the world.
I applaud Hannaford’s efforts at environmental progress, but certainly they could use some help in educating their listeners. Maybe I’m splitting hairs too much and looking too deeply into meaningless ad banter. Then again, that’s what we old fogies are supposed to do.
Poor Steorn. Their machine wasn’t able to handle the spotlight. Literally.
Sean McCarthy CEO stated that “technical problems arose during the installation of the demonstration unit in the display case on Wednesday evening. These problems were primarily due to excessive heat from the lighting in the main display area. Attempts to replace those parts affected by the heat led to further failures and as a result we have to postpone the public demonstration until a future date.” (link to press release)
While I’m completely skeptical about how this “free energy” is supposably obtained, I still really want to see the demonstration. I’m curious to see what kind of contraption they’ve concocted, and what exactly is so special and ground-breaking about it. Nutty ideas sometimes do lead to legitimate and inventive applications, even though the applications may have absolutely nothing to do with the original idea.
Thought is never a bad thing.
Did you ever have one of those moments of extreme and utter stupidity where you have no choice but to drop your face in your open palms and exclaim loudly, “DUH!”
About a year ago I acquired all kinds of electrical meters. There are ammeters (devices that measure electric current), galvanometers (like ammeters but for very small amounts of current), and voltmeters (devices that measure electrical potential difference, sometimes called voltage).
While cleaning out my lab on Wednesday I decided to test out a few. I pulled out an ammeter. The scale read 0-50 milliamps, which is a fairly moderate range as current goes. I have a 9 V battery, and I decide to test the ammeter.
The amount of current that flows in a circuit depends on the battery’s voltage. The more voltage, the more current.
More importantly, though, the amount of current depends on the electrical resistance of the elements in the circuit. Attaching the positive terminal of a battery directly to the negative terminal of a battery is called a “short circuit” — there’s essentially nothing to resist the current’s flow. The current ramps up to very, very high levels.
To limit the current to within the range of the ammeter, I’m going to need a resistor. I do a quick calculation: Ohm’s law states that the current is equal to the voltage divided by the resistance. I find a 220 ohm resistor and plug its value into the equation: current = 9 volts divided by 220 ohms = 0.041 amps = 41 milliamps. Perfect.
I attach a wire from the positive terminal of the battery to the resistor and another wire from the resistor to the negative terminal of the battery (but I don’t complete the circuit yet). I then attach a wire from the positive terminal of the ammeter to the positive side of the resistor, and another from the negative terminal of the ammeter to the negative side of the resistor.
Once I’d finished completing the circuit, I attached the wire from the resistor to the negative terminal of the battery, completing the circuit.
The pointer on the ammeter flung itself so hard to the right and off the end of the scale that the needle actually snapped right off! Freed from the tyranny of measuring current it slid vertically down the front of the ammeter into its eternal rest.
“What the heck happened?” I thought to myself. Is the scale of the ammeter wrong? Why did so much more current go through than I calculated?
Astute readers above would notice that I attached the ammeter around the resistor, in parallel. As I carefully tell my students, ammeters are to be connected in series. Ammeters themselves have a very, very tiny electrical resistance (much less than 1 ohm). By attaching it in parallel, I supplied a second path for the current to travel. The current could take the less-than-one-ohm resistance path or it could take the 220 ohm resistance path. Almost all the current flowed through the ammeter, subjecting it to an exceptionally high current. Certainly more than the 50 milliamps it was rated for.
The ammeter I was using was probably at least 30 years old. Newer devices (some, anyway) try to protect you from yourself to some degree. Modern multimeters are fused — if I’d made my little mess-up with a new-fangled device, I would have blown the fuse but the meter itself would probably have escaped unscathed.
In my brain, I know what happened. I had convinced myself that I was attaching a voltmeter, which is hooked up in parallel. I just got “lost in the moment” and wasn’t paying attention.
There are a couple things to be learned here.