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    Difference: Dielectric and Insulator?

    What is the difference between the terms insulator and dielectric? what do they mean?

    Is capacitor as a whole a dielectric or the air between the plates alone called dielectric? And how is semiconductor related to either dielectric of insulator??
    thanks in advance!

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    Re: Difference: Dielectric and Insulator?

    no difference
    A semiconductor have electrical conductivity intermediate between a conductor and an insulator.



    •   Alt12th March 2012, 13:10

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    Re: Difference: Dielectric and Insulator?

    The term 'dielectric' tends to be used for an insulator that is used where it can be polarized by an electric field, as in a capacitor, and where that is important to the function or needs taking account of.

    It is also applied more to materials that have a high ability to be polarized, if talking about the materials themselves.



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    Re: Difference: Dielectric and Insulator?

    Is it then right to say an insulator always remains a "non-conductor" of electricity/heat, Whereas a dielectric can store charge if maintained at the right potential??
    ANd so is Air an insulator or dielectric?



    •   Alt13th March 2012, 15:05

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    Re: Difference: Dielectric and Insulator?

    "A true insulator is a material that does not respond to an electric field and completely resists the flow of electric charge. In practice, however, perfect insulators do not exist. Therefore, dielectric materials with high dielectric constants are considered insulators." (from wiki)
    Air is a dielectric.



    •   Alt13th March 2012, 15:11

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    Re: Difference: Dielectric and Insulator?

    "Insulator" or "Dielectric" depends largely on the context in which the material is being discussed.

    Mica is a very good electrical insulator - it is often used as such in heat sink mountings. It is also used as the dielectric in mica capacitors. So, which is it? Both, depending on the context. So is air.


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    Re: Difference: Dielectric and Insulator?

    gauthamtechie,

    What is the difference between the terms insulator and dielectric? what do they mean?
    An insulator is a substance that holds onto its valance electrons tightly, so very few charge carriers are available to support conduction. A dielectric is capable of being polarized, i.e., one side of its molecule has a different charge than the opposite side. This forms a electrostatic dipole that increases the capacitance of a capacitor. Those terms are not interchangable. A dielectric must also be an insulator within its voltage range or the cap is considered "leaky". I don't know of any really good insulators that are also really good dielectrics.

    Is capacitor as a whole a dielectric or the air between the plates alone called dielectric? And how is semiconductor related to either dielectric of insulator??
    thanks in advance! .
    As a whole, no. A cap has plates, leads and a protective coating besides a dielectric. A vacuum, also known as "free space", has a relative dielectric constant (also known as relative permittivity) of 1. The dielectric of vacuum is the standard for which other materials are compared. Air has a dielectric constant close to 1, mica is 6.0. A material that polarizes easily makes a better dielectric. In a parallel plate capacitor, the capacitance is directly proportional to the dielectric constant.

    A semiconductor is ultra pure crystalline silcon to which a controlled relatively small amount of "dopant" is added. This makes it conduct it better than a insulator but less than a metallic conductor. It would not be a very good dielectric because it would leak badly. It goes beyond the scope of your question to discuss semiconductors further.

    Is it then right to say an insulator always remains a "non-conductor" of electricity/heat, Whereas a dielectric can store charge if maintained at the right potential??
    ANd so is Air an insulator or dielectric? .
    Any insulator will pass a minute amount of charge if the voltage is high enough. A dielectric does not store charge. As part of a capacitor, it stores energy. The amount of charge carriers in a cap at 100 volts is the same as at 0 volts, but the energy stored is much higher. A capacitor is never "charged", it is energized.

    poluekt ,

    Therefore, dielectric materials with high dielectric constants are considered insulators." (from wiki)
    Nope, the dielectric constant and conductivity are two independant parameters. If Wiki said that, they are wrong. A high dielectric constant means the material polarizes easily.

    Air is a good insulator, but not much better than vacuum for dielectric constant value.

    Ratch
    Last edited by Ratch; 9th April 2012 at 21:16.


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    Re: Difference: Dielectric and Insulator?

    thank you, that has clarified many things.

    Also, i just want to know if i got this right:
    Quote Originally Posted by Ratch View Post
    Any insulator will pass a minute amount of charge if the voltage is high enough. A dielectric does not store charge. As part of a capacitor, it stores energy. The amount of charge carriers in a cap at 100 volts is the same as at 0 volts, but the energy stored is much higher. A capacitor is never "charged", it is energized.
    This is something that's new to me: You're saying capacitor does not store charge? But then i've heard about these terms "capacitor discharges" et al. Oh so then May i presume by "discharging", They mean it becomes "de-energized"?

    Finally, you are saying in a capacitor, some "x" coulombs of charge is present at any voltage. And at 100 volts, what becomes higher is not the "coulombs" but the "workdone" which is Joule per coulomb (J/C) ,right?



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    Re: Difference: Dielectric and Insulator?

    gauthamtechie,

    This is something that's new to me: You're saying capacitor does not store charge?
    Correct, its net charge remains zero before and after any voltage is applied. Before any voltage is applied, the charge difference between the plates is zero. After applying any voltage, there is a charge difference between the plates, but the net charge is still zero. The excessive charge on one plate is balanced by a deficient charge on the opposite plate for a net charge change of zero. It takes energy to separate the charges, and anytime unbalanced charges are present, an electrostatic field is formed. The energy or work it took to separate the charges is stored in the electrostatic field.

    But then i've heard about these terms "capacitor discharges" et al
    Yes, and you heard NASA saying that they "walk" in space, too. You've seen video of astronauts outside their spacecraft. Are they walking?

    Oh so then May i presume by "discharging", They mean it becomes "de-energized"?
    That is 100% correct.

    Finally, you are saying in a capacitor, some "x" coulombs of charge is present at any voltage.
    The charges on the plates of a cap are either in balance with each other, or there is a difference as explained above.

    And at 100 volts, what becomes higher is not the "coulombs" but the "workdone" which is Joule per coulomb (J/C) ,right? .
    There would be a coulomb difference between the plates of the cap. Joules/coulomb is the energy density of the charge, or voltage. So both the voltage and energy of the capacitor increase, and the net charge stays the same.

    Ratch


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    Re: Difference: Dielectric and Insulator?

    You've nailed it

    Are you a professor ?



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    Re: Difference: Dielectric and Insulator?

    guanthamtechie,

    You've nailed it
    It is all a matter of disregarding the false jargon. Otherwise descriptions get confused. In physics, it helps to use precise explanations and disregard analogs unless you are trying to make a point.

    Are you a professor ?
    No, I just try to arrange facts so they make sense.

    Ratch



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