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Does My Bike Induce Electricity?
An anonymous reader asks: "I have a steel frame road bicycle and recently began riding on a path that parallels high-tension power lines for several miles. My question is: Does my bike induce an electric current by passing through the electric fields from the power lines? I normally ride the section at about 18 miles per hour, estimate the distance to the lines at about 75-100 feet, and think they're 200KV lines."
Last year my physics teacher told me a story about a guy who was stacking hay bales under power lines. These weren't super-powerful powerlines, just regular ones alongside the road. Anyhow, the guy had a nice stack going when he was blown off his tractor by some mini lightning caused by the hay powerlines.
The way he explained it, the hay on the ground built up a charge and it was just a matter of time before it discharged with the power lines. When he was stacking, he must have gotten the charged hay too close or something, and it shocked him.
I suppose it's possible you're getting a little stray charge, but as long as you're not wearing a suit made of hay...
It is also compressed in the direction of motion, warps time, and emits graviton pulses.
Translational symmetry guarantees that as you move parallel to the cables, nothing happens.
:)
Physics seems to provide an endless supply of April Fool's jokes!
Time to post that 'Evil bit' article again!
-- Cheers!
Do you notice a dull glow radiating from your body when all the lights are off?
No Comment.
Eureka!
Now we know why they run power lines alongside every road -- so they can soak up the free energy caused by cars driving alongside them!
Answer: Yes. Is it enough to matter? No.
i was once standing in a river holding onto an aluminum canoe near some high tension lines and i could definitely feel current when i touched the canoe and none when i let go
You can increase the induced emf by wrapping multiple turns of insulated magnet wire into a loop in the same orientation as the bike frame. Neglecting the finite resistivity of the wire, you will get twice as much emf every time you double the number of turns. But even with hundreds of turns we're still talking about millivolts or perhaps hundredths of a volt at most.
If the line is DC, then there will be no induced emf since the magnetic field is not changing.
The speed at which you ride the bike has no influence on the induced emf, unless you are travelling near light speed, in which case the apparent frequency of the AC will be reduced since you are "catching up" to the propagating waveform. But I don't think you could pedal that fast :-)
Even better some night take one of those 5 foot lone florecent tube light bulbs (the kind in most schools and offices) and hlod it under the power lines....it'll light up. I've seen this done with the HIGH power lines. It's freaky.
I was once exiting a movie theater in a drizzle. This particular theater's parking lot is under high-tension transmission lines. Since it was raining, I was using an umbrella.
Walking across the parking lot, I heard a buzzing sound. Looking up, I noticed that where the metal ribs of the umbrella connected to the plastic hub in the center, that the tips of the ribs were arcing between them!
Surprisingly enough, I merely thought it curious and noted that I should go back some time and study the effect further and take some measurements, etc. That was probably a dozen years ago, and I pretty much forgot about it until this story prodded my memory.
I assume that some sort of "Tesla" effect was responsible, as I felt nothing myself. I don't know the specifics of the transmission lines involved.
alright, I'm a long way from being an EE, but I remember my high-school physics pretty well.
a magnetic field will form in concentric rings around any conductor that's carrying current, and the strength of that magnetic field will be proportional to the amount of current flowing through the conductor, and will drop off sharply with distance.
now, currents are only induced by a changing magnetic field, and the current will be proportional to the change in magnetic field strength. so if the power lines were carrying DC, and you were riding parallel to the lines, no current would be induced in you because the strength of the magentic field where you were riding would stay about the same -- but the power lines are probably carrying AC, so even if you stay still, the magnetic field will be reversing polarity every 1/60th of a second, and a current will be induced in you.
however, there are a few mitigating factors.
one is that you're probably several meters away from the lines, and magnetic fields don't couple well through air. transformers often have an iron core to guide the magnetic field between the two coils, because otherwise not much power gets transferred between them.
another factor is that the magnetic field around a single conductor is not very strong, unless it's carrying really a lot of current (like wire-melting amounts). again, transformers and electromagnets use coils with hundreds or thousands of turns to get a decent magnetic field going.
the last factor is that the lines are carrying high voltages. the comment in your submission seems to indicate that you think this will create a stronger magnetic field, but actually the opposite is true. for our purposes, electric power has two aspects, voltage and current; the voltage determines the strength of the electric field, and the current determines the strength of the magnetic field. for the same amount of power, if you increase the voltage, you reduce the current. the power company doesn't want current being induced in random objects, because that power gets lost as heat and costs them money (actually, they probably care more about the fact that large currents create heat in the wire itself -- but it works out to the same meaning for you). they run long lines at very high voltages as part of a strategy to minimize this power loss and save money.
practically no. There are several factors at work here. First of all is that in order to create electricity a conductor (your bike) must move perpendicular to the magnetic field. By riding parallel to the power lines you are, in effect, riding parallel to the magnetic field. However, since the power lines cary AC current the magnetic field is expanding and collapsing around you so your bike is moving (or rather the magnetic field is moving) through the magnetic field. Secondly the generation of a magnetic field around a wire is a function of the amount of power (Voltage * Current) in the wire. In other words a wire that is carrying 200K Volts but very little current, say 0.005 Amps would have a smaller and less powerfull magnetic field than a wire with 12 Volts carrying 200 Amps. Thirdly the Inverse Square Law takes affect in this situation. Simply put, it states that the magnetic field is reduced in strength proportional to the sqaure of the distance you are from the wire. If you are 4 feet from the wire the strength of the magnetic field is a factor of 16 less than the maximum (right at the wire). At 5 feet the factor is 25, at 6 feet the factor is 36 etc.
Meddle thou not in the affairs of Dragons, for thou art crunchy and with most anything.
"the transmission line it creates a magnetic field perpendicular to the wire"
The electric field from a charge will be perpendicular to the charge. The magnetic field follows the old "right-hand rule" and circles the current. This would still imply that the field is going throught the frame of the bike but....
One should not theorize before one has data. -Sherlock Holmes-
The reason power is transferred via high volatage AC power, and not any kind of DC power is simple:
The lower the current you send down a wire, the less energy lost due to resistance. (P=IE, E=IR, so P=R*I^2). This is a major concern over long wires, where the overall resistance can be quite high. With AC power, you can transform from high current / low volatage, to low current / high voltage, and back quite easily. So you can put your powerplant far away from the consumer. However with DC, you can't do this. DC can't be transformed (at least, not easily?), and so you have to run it down the powerlines at the same voltage/current as the consumer will use, which is quite high. Hence, you loose a lot of energy on powerlines very quickly, and thus your powerplant must be close (within a couple miles actually) of the customers.
I should also mention (although I think I see posts saying this later on) that, indeed, the bike is a one loop conductor, and that the powerlines (via the right hand rule) have a varying magnetic field (because the current is varying), but the induced emf is very small. This is because the current in the wires is small, and there aren't very many of them, and you are 50+ ft away, and your bike is only one loop. I'd call the induced emf negligable personally.
-Jeff
Physicist, Programmer
Yes, you do in fact get an induced current. However, as demonstrated vividly by a question on my final when I was taking first semester E&M, you need somewhere on the order of 200,000 loops of wire to get enough induced current to be worthwhile from 20,000V power lines. (The exact question was, is it feasible to steal power by placing a coil between two 20,000V power transmission lines.) I'm pretty sure you don't care about the negligible effects (unless you're paranoid, or your bike is composed of 200,000 loops of wire).
There's no sig like SIGSEG
wire who used the power bleeding onto his property to run the dishwasher is any indication, you'll be going to jail for the power you're stealing too.
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