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What can induce electron flow?

  1. Jul 9, 2013 #1
    I can think of three ways to induce electrons to flow and generate electricity:

    1. Light (i.e. PV cells)
    2. Catalyzed chemical reaction (batteries, fuel cells)
    3. Magnetic field (turbines -- gas, wind, water, nuclear... everything else I can think of)

    Mostly turbines. I was wondering if anyone could at to the list? Or could explain why magnets are so dominant?
  2. jcsd
  3. Jul 9, 2013 #2


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    Gold Member

    Well.. turbines are only responsible of creating a rotating field - as only non-stationary field can create current flow (voltage actually -> Faraday's Law of Induction).

    Why turbine + magnets (electromagnets, permeant magnets) are dominant ? Because it's cheaper to produce power this way. Large power density (~few W\kg).
  4. Jul 9, 2013 #3


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    Staff: Mentor


    Piezoelectric materials


    Kelvins water dropper, cat fur

    Electric eels :smile:
    Last edited: Jul 9, 2013
  5. Jul 10, 2013 #4
    Well, when it comes to just causing electrons to flow, there are 6 ways I know of (general.)

    Heat (thermocouples,) pressure (some crystals etc,) friction (static,) chemical (batteries,) solar (light,) and I believe the last one is magnetic.

    I would post a more in depth explination but I am on my phone. I can add more of an explination later.
  6. Jul 15, 2013 #5


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    Certainly the most popular way to generate electricity is to rotate a magnetic field around a wire....also known as a generator. I would assume this generates at least 90% of the worlds power.

    What drives that generator can be a number of things. Boiling a gigantic pot of water (usually heat created by coal or E=mc^2) and using the steam to drive a generator I would also think powers at least 90% of the worlds power. These giant pots of water can be 15 stories high and even higher.

    Gigantic water falls (Hoover dam for example) also make a lot of power by turning generator. And these are certainly the best since the power source is free and the pollutants are near zero.

    Wind turbines are inefficient, expensive and not overly impressive at this time.

    All other forms are certainly important, but just subsets at the moment compared to the dominant rotating magnetic field.
  7. Aug 1, 2013 #6


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    I would say that this is because magnets are easy to manipulate mechanically, and any movement of a magnetical field entails a movement in an electric field.

    Most of the energy generation methods used on a large scale involve a change of energy from one form (chemical, mass, kinetic) to kinetic; e.g. Chemical energy in coal is released as heat which is then converted to kinetic energy in steam.

    Magnets seem to me to be the only to convert large amounts of kinetic energy into an electric current.

    I question both statements. While the running of HEP stations does not require much energy input or pollutant output, the construction of a "gigantic water fall" involves "gigantic" amounts of concrete. Hoover dam, being your example, contains some 2,480,000 m3 of concrete. As concrete sets a chemical reaction takes place, emitting heat and carbon dioxide.


    Hence the total amount of carbon dioxide emitted from the Hoover dam during construction could be in the region of 1,016,800 tons. I'm not saying HEP is an environmental disaster (quite the contrary) but don't be ignorant of it's impacts!

    "Wind turbines are inefficient, expensive and not overly impressive at this time."

    Typical commercial turbine: 2 MW in size and cost roughly $3-$4 million installed, which would be expected to run for about 120 000 hours. That's ~240,000,000 KWh, so roughly $0.016 per KWh. But I fear this is an under estimate, as NO wind turbine constantly runs at rated power, or anywhere near it!


    Suggests $/KWh for wind is $0.097, so I was out by a factor of about 6 :biggrin:

    Any way to the point... Natural gas is cheapest per unit energy, then HEP, then wind. So wind is not overly expensive.

    Wind cannot be >56% efficient due to Betz' law, which basically uses the idea that the more efficient your wind turbine the slower the air after your turbine, which in turn slows the air before the turbine (which in turn lowers your power output). Read up on it, it's a great proof!
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