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."

Comments

No...

[Anonymous Coward]

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! :)

another shocking anecdote...

[cryptozoologist]

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

[pclminion]

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 :-)

Re:Cars

[The_K4]

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.

An Interesting Incident

[dmadole]

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.

In theory yes

[Y Ddraig Goch]

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.

Re:Aha!

[pclminion]

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 effect is tiny, but nearby metal objects actually *reduce* the efficiency of the transmission.

Yes and if that guy with the barrels full of...

[Deanasc]

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.