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It's funny. Laugh. Science

Does My Bike Induce Electricity? 72

Posted by Cliff from the hidden-dangers-of-electrical-fields dept.
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."
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Does My Bike Induce Electricity? More

Does My Bike Induce Electricity?

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  • Frankly i doubt it, there must be significant regulation regarding high voltage power lines and how high they must be, so i think they're far enough away that they wouldn't cause any trouble.
  • Think how much caars would induce if your bike induced enough to tell about
    • Turn on the radio and go under the powerlines, what do you hear? Induced current on your antenna? :) Maybe not...

      • Re:Cars (Score:3, Interesting)

        by The_K4 ( 627653 )
        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.
        • Recently I was replacing the backlight in a laptop's LCD screen. I bought the backlight (which is a thin, cold-cathode flourescent tube - about 3mm in diameter and 200mm or so long) from Fry's Electronics, and brought it home in the plastic bag. I took it out of the bag (but still in its package) and walked across the room - and it flashed briefly, but brightly. At first it startled me, then I realized that the static electricity buildup was discharging in the tube. I found that you could crumple up the pla

  • combusting hay (Score:3, Funny)

    by bryanthompson ( 627923 ) <logansbro.gmail@com> on Tuesday April 01, 2003 @03:08PM (#5639577) Homepage Journal
    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...

  • Yes (Score:4, Funny)

    by LarryRiedel ( 141315 ) on Tuesday April 01, 2003 @03:09PM (#5639595)
    It is also compressed in the direction of motion, warps time, and emits graviton pulses.

  • No... (Score:3, Interesting)

    by Anonymous Coward on Tuesday April 01, 2003 @03:10PM (#5639608)
    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! :)
    • Not true if it is an AC transmission line. In that case, even if you sit still, the alternating current will cause the magnetic field inside the conducting loop of your bicycle frame to vary and change direction. This will induce an emf and drive a current in the frame.

  • Hey Taco (Score:4, Funny)

    by tsa ( 15680 ) on Tuesday April 01, 2003 @03:12PM (#5639624) Homepage
    Time to post that 'Evil bit' article again!

  • Dull glow? (Score:3, Funny)

    by GeckoX ( 259575 ) on Tuesday April 01, 2003 @03:13PM (#5639638)
    Do you notice a dull glow radiating from your body when all the lights are off?

  • Aha! (Score:3, Funny)

    by TheSHAD0W ( 258774 ) on Tuesday April 01, 2003 @03:15PM (#5639647) Homepage
    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!
    • Didn't we just have the Perpetual Motion Slashdot article? Maybe someone needs to try this method. "Power lines" doesn't sound as mysterious as "ether" ... but you work with what you're given.

    • Re:Aha! (Score:3, Interesting)

      by pclminion ( 145572 )
      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!

      Actually, the magnetic field of the AC line will induce eddy currents in the body of a passing car. These eddy currents produce their own magnetic fields which oppose the field from the wire, and these fields actually reduce the current flowing in the wire (the energy to produce the eddy current has to come from somewhere, that somewhere is the current in the wire).

      The

  • Dorm session question (Score:2, Informative)

    by crmartin ( 98227 )
    Answer: Yes. Is it enough to matter? No.

    • Re:Dorm session question (Score:3, Informative)

      by KDan ( 90353 )
      More detailed answer:

      Yes. The current goes around in circles in the steel frame your wheels (eg arc-on-outside/radius/central-bit/radius/etc - like a pie slice). Depending on the exact configuration you might be able to power a very small light bulb from it. I wouldn't bet my hand on it though.

      Daniel
  • A question from the Phys 253 final (Magnetism final.)
  • The amount of electrical energy you'd get would be minute. You might be able to run an LED for a bit if you built up a charge on a capacitor for a few minutes. I'd worry more about the magnetic fields from the power lines affecting your brain's alpha waves. :-)
  • used to act funny on foggy days near the high tension lines on powerline trail in Gorman Ca. Splutter, splutter, cough, choke, brrrrrrrrrrrrr, brrrrrrrrrrrrrrrr.
  • 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

  • Depends (Score:5, Interesting)

    by pclminion ( 145572 ) on Tuesday April 01, 2003 @04:03PM (#5639998)
    If the lines are AC (which is the usual case except for long distance transmission lines) then you should have an induced emf in the bike frame. The bike frame forms a conducting loop, and as the AC current oscillates in the transmission line it creates a magnetic field perpendicular to the wire, which oscillates at the same frequency. As this magnetic field passes through the bike frame loop it will induce an alternating current at the same frequency. Basically your bike frame is acting like a single-turn inductor.

    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 :-)

    • If the line is DC, then there will be no induced emf since the magnetic field is not changing.

      But he's moving relative to the wire.
      • But he's moving relative to the wire.

        That doesn't matter, because he's moving along parallel to the wire. The magnetic field is perpendicular to both the wire and the direction of travel, so the field strength is independent of the motion. If he were moving obliquely w.r.t. the wire then the field *would* depend on the motion and you would see an emf.

        • Huh. Guess you learn something every day.

          If that's the case, AC induces, DC doesn't, then how come AC is used for long distance lines? It seems like you'd want the transmission method that *doesn't* induce current in everything near the line.
          • If that's the case, AC induces, DC doesn't, then how come AC is used for long distance lines?

            You answered your own question. It's precisely *because* AC induces that it's used for transmission. Induction is what makes transformers possible. DC current can't be easily converted from one voltage to another the same way AC can.

            The powerlines you see around your neighborhood are 12-20 kV, 50 or 60 Hz. For efficiency reasons, power is transmitted at the highest possible voltage (this reduces resistive loss)

        • The magnetic field is perpendicular to both the wire...

          Naw, the magentic field lines are found by using the "right hand rule" (or the left hand rule if you're an EE guy). So the field lines wrap around the wire. But he still isn't 'cutting' any of the lines by riding parallel to the wire (aka moving between different potential levels in the field). Just a techincal note.

          neurostar
          • Naw, the magentic field lines are found by using the "right hand rule" (or the left hand rule if you're an EE guy). So the field lines wrap around the wire.

            Right, they "wrap around" the wire. Although the field lines are curling around the wire, they are still always perpendicular to it (dot product of magnetic field and current is always zero). The field lines are tangentially perpendicular, not radial.

    • "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....
    • 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

      • 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.

        Actually, it's not negligable. I used to ride

        • Now I'm curious to pump through the equations and see. :) ( Haven't done induced emf since I taught it to my lab students *last* April. :) Been focusing on thin films coatings, at the company I work for, these days.)
        • Actually, it's not negligable. I used to ride my bike for a kilometer or two quite often under some 115 kV lines near where I lived. If i didn't ground out my bike, or touch it every 10 seconds, I'd get quite a shock..

          I believe this is possible, but this wasn't caused by induction. The induced emf due to the transmission wire's magnetic field will create a current in the bike frame, but this current is just a loop, and can't cause charge to build up on the bike.

          What happened to you was an effect of the

    • I should have thought of this example a couple months ago when I was teaching introductory analog circuits. This would have made a really great qualitative final question!

      I could have used your post for the key too.
    • Uhh... transmission lines are AC.. even long distance high-tension lines... ESPECIALLY long distance, high tension lines.

      There would indeed be some current in the bike. IF you actually used it, though, causing a power drain, you would be stealing power from the power company, and probably labeled a terrorist ;)
      • Uhh... transmission lines are AC.. even long distance high-tension lines... ESPECIALLY long distance, high tension lines.

        Ok, then what is this [hydro.mb.ca] and this [siemens.com] and this [nexans.no] and this [fujikura.com] and this [stantec.com]?

  • An Interesting Incident (Score:3, Interesting)

    by dmadole ( 528015 ) on Tuesday April 01, 2003 @04:12PM (#5640059)

    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.

    • 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!

      Mmmm... rib tips.

      (C'mon, it's more on-topic than all the dupe complaints today ;)
    • 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!

      I had this happen too. Try less 'shrooms and more Kool Aid next time you see The Wall at the $1 theater.

  • 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 c

    • This topic brings up an interesting question...

      How much energy could you extract from these powerlines using a device which you could carry with you while walking on the ground below them? Would it be enough to power an LED like you see on some cell phone antennas? More? Less?

      • You could build a device that would be able to power a LED while standing under high tension power lines. What you need is a big coil of wire. It probably would not be particularly practical to carry though. A senior year engineering project was (in essence) to construct a device to measure the magnetic field under high tension lines. The device had to use 2m diameter coils to be able to reliably measure the induced voltage. Based on that work I suspect that a coil to power a LED would need to be larger the

  • In theory yes (Score:2, Interesting)

    by Y Ddraig Goch ( 596795 )
    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 magn
    • Your numbers work out....

      200kV @ .005A = 1000W
      12V @ 200A = 2400W

      But your premise is false.... stepping up the voltage does not reduce the amount of power available.. it remains constant (barring loss due to to other stuff). And those high voltage transmission lines have a lot more power than the low voltage in your house, as they are later broken down into smaller, lower voltage, lower power chunks for different homes.

  • "Does my bike induce an electric current by passing through the electric fields from the power lines?"

    Not so much induce as have induced in it. Your bicycle's steel frame, an electro-magnetic conductor, could have a current induced in it if it is in motion relative to a magnetic field( field stationary, bike moving, bike stationary, field moving). Because the field is expanding and collapsing at 60 cycles per second it would be in motion relative to your bike whether your bike is moving parallel to the po

  • Yes, but it's negligible (Score:4, Informative)

    by muon1183 ( 587316 ) <(muon1183) (at) (gmail.com)> on Tuesday April 01, 2003 @07:06PM (#5641117) Homepage
    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).

  • Yes and if that guy with the barrels full of... (Score:3, Interesting)

    by Deanasc ( 201050 ) on Tuesday April 01, 2003 @07:13PM (#5641145) Homepage Journal
    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.
  • While passing your STEEL bike in and out of electric and magnetic fields WILL IN FACT produce a current there is nothing to worry about. It really does not matter. In fact, electric / magnetic flux lines running IN and OUT of your bike will cancel each other out. Hence there will be NO buildup of charge and that is precisely why you have not noticed anything. On the flipside, because you are travelling parallel to the power lines you really arent changing your electric field potential from the source.

  • Don't forget it's a three-phase line (Score:1)

    by Anonymous Coward
    Actually, the overhead line consists of three wires. The sum of the current in these wires is always zero! So at sufficient distance (i.e. at ground level) the magnetic field resulting from these lines will be extremely small - MUCH smaller than if only a single wire was present.
  • Has anyone forgot that the bike (unless we're talking about ET) is in constant contact with the ground. This means (even though the tires are rubber) any excess electrons you are receiving from the power lines will be transmitted into the ground. Therefore your charge in the bike and yourself should remain neutral most of the time. Of course this is all electrostatic charges vs. the current from the wire.
    • Actually, you aren't receiving any electrons from the lines. What is happening, is you are cutting the flux lines of the electricity, inducing a current in your bike (or whatever metallic object, be it a car, or whatever). This is part of Faraday's Law/Lenz's Law. The fact that mere micro-volts at most would be produced, is a testament to the fact that the electrons motion (induced by the electro-magnetics field of the H-V transmission lines) would not be nearly enough to ground out (because the breakout
  • Back in high-school physics, we tried taking one of those 4' fluorescent tubes that everybody uses to light schools and offices out to the high-tension wires near my house. The induced potential difference if the tube was held vertically under the wire (at ground level under one of those massive steel-girder towers) was enough to light it dimly. But we're not dead. So you should be fine.
  • When aircraft fly through the Earth's magnetic field, there is a detectable potential difference between the wingtips, enough to have to correct for it on the magnetic field-sensitive instruments.

    The current is negligable, but it's there.

    So, by moving through the Earth's field you'll be inducing a voltage, but it's going to be extremely small.

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