what is the difference between insulators and dielectrics?:
Insulators have there dielectric constant as 1 but if you are talking about a normal dielectric than it could have dielectric constant between 1 and infinity.
they are the same
I disagree. it is correct to say that all dielectrics are insulators; but there are insulators that are not (usually) referred to as dielectrics.
A good example would be Mott insulators (I can also think of other examples, e.g. metallic superinsulators).
Note the "usually" above, I have heard of people referring to Mott insulators as dielectrics; but it is pretty uncommon and there is a case for reserving the word "dielectric" for materials which are insulating due to their band structure.
From a fundamental point of view, every substance is a dielectric, i.e. it has a dielectric constant, whether conducting or isolating. However, this term is usually used in a technical context, e.g. referring to materials used to build a condenser. In these technical applications, the material shouldn't be conductive, for obvious reasons.
I've given an answer without any context, the same way the OP didn't bother to provide any context to the question. I only thought it is fair, and if the answer appears to be too simplistic and ambiguous, so was the question.
I also highly doubt that the OP has any idea, or that this question is really focusing, on Mott insulators. Speaking of which, Mott insulators ARE dielectrics in the sense that they are also ceramic insulators. We speak of them as being "dielectrics" or "ceramics" or "insulators" interchangeably.
I also disagree with the equivalence for somewhat pedantic reasons. While the terms are almost always used interchangeably in the field, they refer to different underlying electronic properties. A good insulator is therefore a material with low conductivity while a good dielectric is a material with high polarizability. Of course, a dielectric used in a capacitive role is almost always preferred when it also has lower conductivity.
I don't think the question was so focusing to answer as previous answers (make thing complicated) and also he ask about the material that is decrypted as dielectric or insulator and we know that in our lectures we use them interchangeable.
First: I think this is really the best answer detailing the slight difference.
But isn't a dielectric almost always used in some sort of capacitive role, hence a good one needing a high polarizability?
It seems to me that the difference is almost always unnoticeable and unimportant.
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