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Volts per metre

Discussion in 'General Electronics Discussion' started by Rajinder, Jan 21, 2018.

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  1. Rajinder

    Rajinder

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    Hi all,
    I have a question regarding volts per metre or v/m.
    I know that this is a unit to measure electric field strength/intensity.
    I believe thst when we say 1V/m it means at a distance of 1 metre a voltage of 1V strength is applied. I also know it is used in EMC immunity tests.
    My question is that how could i relate the meaning of V/m in a way that would be easily understandable. What would 1V/m be equivalent to in simply terms thst could be understood by a non electronics person.
    Thanks in advance.
     
  2. davenn

    davenn Moderator

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    The standard unit of electric field (E-field) strength is the volt per meter (V/m). An E field of 1 V/m is represented by a potential difference of 1 V existing between two points that are 1 m apart.

    how's that ? cant get much simpler :)
     
  3. Rajinder

    Rajinder

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    Jan 30, 2016
    Thanks for the reply. But how can i equate this to simpler terms for non engineers. What is 1V/m equivalent too? What is the field intensity equivalent too.
     
  4. davenn

    davenn Moderator

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    it's as simple as that, don't know how to make it any easier :)

    Dave
     
  5. Rajinder

    Rajinder

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    Ok but what wiuld the field strength of 1V/m be equivalent to? Thats what i am really asking.
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    It is equivalent to 1mV per mm, or 25.4 mV per inch.

    If you want it in more fundamental units, then 1V/m is 1 (kg.m)/(s3.A). I'm not sure that's what you want.

    It's the same electric field generated by a 1.5m long 1.5V battery.
     
    Rajinder likes this.
  7. Rajinder

    Rajinder

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    Yes this us what i want. Trying to relate this to something equivalent. Please could you shiw me how you came across the 1.5m long 1.5V battery.
    Thanks
     
    Merlin3189 likes this.
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    That was a bit of a joke.

    1V/m is equal to xV/xm. If x is 1.5, you get 1.5V per 1.5 metres.
     
    Arouse1973 likes this.
  9. hevans1944

    hevans1944 Hop - AC8NS

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    Real-world example however, which is what the OP is asking for.

    Geez, @Rajinder, do the math: 1.5 volts between the opposing (oppositely charged) end terminals of a 1.5 meter long battery is... duh! One volt per meter.

    The electrical field strength existing in the atmosphere is about 100 volts per meter near the surface of the Earth under fair-weather conditions, caused by world-wide lightning discharges occurring at a rate of approximately sixty per second, that "charge up" the conductive ionosphere. You don't "feel" this electric field because the human body is conductive and "shorts out" the electrical field because the source impedance of the electrostatic field through the air is very large. It is easily measured, however, with a high-impedance electrometer connected to a pair of probes. Go to this Google results page for more information. Remember: voltage does not exist at a point, it is always measured between two points a finite distance apart.

    The electric field is a vector field with magnitude and direction (polarity) that fills all of space. Clearly, the electric field has a value at any given point is space, but for practical purposes all you can measure is the gradient of that field... in volts per meter. The field itself can be defined as the force exerted on a "test charge" placed in the field, that is, the force per unit charge, but it is usually impractical to measure that. Compare with measuring the Earth's gravitational field which could be defined as the force exerted on a "test mass" placed in the field, that is, the force (weight) per unit mass.
     
  10. AnalogKid

    AnalogKid

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    Think about a rubber band stretched until it is 1 m long. The tension between the endpoints is 1 band per meter. Now pull two identical rubber bands; that pulling force is 2 bands per meter.

    Note that this analogy does not travel well. Stretching 1 band to 2 meters doubles the force, while moving two points with 1 V potential difference from 1 m apart to 2 m apart cuts the field strength in half.

    A better analogy that is harder to visualize is some kind of compressible medium, like a giant kitchen sponge. Pressing on it until it is 1 m long takes some force. Continuing to press on it until it is 1/2 m long takes twice as much force. 1 V/m is 1/2 the field strength of 1 V/.5m.

    The problem with this analogy is that electromotive force actually tries to push electrons from the - point to the + point (or pull from + to -), like the pulling force in the first analogy, rather than push them apart as in the 2nd one.

    ak
     
  11. Rajinder

    Rajinder

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    Sorry i wasnt thinking :)
     
  12. Rajinder

    Rajinder

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    Jan 30, 2016
    Sorry i wasnt thinking :)
     
  13. Ratch

    Ratch

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    Another way to detect an electric field is to measure the force on a charged particle (electron, proton) when the particle encounters an electric field. That is how some CRTs deflect the electron beam. Volts per meter and force per charge both reduce to the same units. I can show you how to prove it if you cannot do so yourself.

    Ratch
     
  14. davenn

    davenn Moderator

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    Thread closed

    answers were given very early on
     
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