how can we define permittivity?

balaji s, 12 years ago

Grade:

2 Answers

Hasan Ali

35 Points

12 years ago

There are many types of primitivity like electromagnetism, permittivity,Vacuum permittivity, Complex permittivity,Measurement etc.

In electromagnetism, permittivity is the measure of the resistance that is encountered when forming an electric field in a medium. In other words, permittivity is a measure of how an electric field affects, and is affected by, a dielectric medium. Permittivity is determined by the ability of a material to polarize in response to the field, and thereby reduce the total electric field inside the material. Thus, permittivity relates to a material's ability to transmit (or "permit") an electric field.

The vacuum permittivity ε₀ (also called permittivity of free space or the electric constant) is the ratio D/E in free space. It also appears in the Coulomb force constant 1/4πε₀.

Its value is^[1]

$\begin{align} \varepsilon_0 & \stackrel{\mathrm{def}}{=}\ \frac{1}{c_0^2\mu_0} = \frac{1}{35950207149.4727056\pi}\ \frac\text{F}\text{m} \approx 8.8541878176\ldots\times 10^{-12}\ \frac\text{F}\text{m} \end{align}$

where

c₀ is the speed of light in free space,^[2]

µ₀ is the vacuum permeability.

Constants c₀ and μ₀ are defined in SI units to have exact numerical values, shifting responsibility of experiment to the determination of the meter and the ampere.^[3] (The approximation in the second value of ε₀ above stems from π being an irrational number.)

The dielectric constant of a material can be found by a variety of static electrical measurements. The complex permittivity is evaluated over a wide range of frequencies by using different variants of dielectric spectroscopy, covering nearly 21 orders of magnitude from 10⁻⁶ to 10¹⁵ Hz. Also, by using cryostats and ovens, the dielectric properties of a medium can be characterized over an array of temperatures. In order to study systems for such diverse exciting fields, a number of measurement setups are used, each adequate for a special frequency range.

plz.... approved my answer......

SAGAR SINGH - IIT DELHI

878 Points

12 years ago

dear student,

Permittivity, also called electric permittivity, is a constant of proportionality that exists between electric displacement and electric field intensity. This constant is equal to approximately 8.85 x 10^-12 farad per meter (F/m) in free space (a vacuum). In other materials it can be much different, often substantially greater than the free-space value, which is symbolized e_o.

In engineering applications, permittivity is often expressed in relative, rather than in absolute, terms. If e_o represents the permittivity of free space (that is, 8.85 x 10^-12 F/m) and e represents the permittivity of the substance in question (also specified in farads per meter), then the relative permittivity, also called the dielectric constant e_r, is given by:

e_r = e / e_o
= e (1.13 x 10¹¹)

Various substances have dielectric constants e_r greater than 1. These substances are generally called dielectric materials, or simply dielectrics. Commonly used dielectrics include glass, paper, mica, various ceramics, polyethylene, and certain metal oxides. Dielectrics are used in capacitors and transmission lines in alternating current (AC), audio frequency (AF), and radio frequency (RF) applications.

Also see farad per meter, capacitor, and electric field.