IIT JEE , AIEEE Forum - Physics , Electricity

arpitsri_2007

1.WHAT IS DRIFT VELOCITY .IT IS UNIFORM OR NON-UNIFORM

IN ITS DERIVATION WHY WE USE BOTH THE EQN OF UNIFORM AS WELL AS NONUNIFORM MOTION.

2.HOW TO DEFINE THE ABSOLUTE ELECTRICAL PERMITTIVITY,ELETRICAL SUSCEPTIBILITY OF A MEDIUM AND HOW THESE DIFFER FROM PERMEABILITY

krishna.gopal

One question at a time
Drift velocity is drift of electron per unit time where drift is difined as position of eectron in electri field with respect to its position had there been no electric feild..
In during motion electron accelerates between collisions but it again attains zero velocity after collision. So when we are talking on time scales of collision times we assume electron to be accelerated and take drift velocity as acc*collision time.Now this velocity will be different for different electrons. It may be different even for same electron in different collisions. So on a large time scale we take average drift velocity and assume it to be constant and hence use equations of uniform motion.

aravindh_ramaswamy

Hi!

Permittivity is a physical quantity that describes how an electric field affects and is affected by a dielectic medium, and 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 electric susceptibility ?_e of a dielectic material is a measure of how easily it polarizes in response to an electric field.. This, in turn, determines the electric permittivity of the material and thus influences many other phenomena in that medium, from the capacitance of capacitors to the speed of light.It is defined as the constant of proportionality (which may be a tensor) relating an electric field E to the induced dielectic polarisation density P such that

${\mathbf P}=\varepsilon_0\chi_e{\mathbf E},$

where $\, \varepsilon_0$ is the electric permittivity of free space.

The susceptibility of a medium is related to its relative permittivity $\, \varepsilon_r$ by

$\chi_e\ = \varepsilon_r - 1.$

So in the case of a vacuum,

$\chi_e\ = 0.$

The electric displacement D is related to the polarization density P by

$\mathbf{D} \ = \ \varepsilon_0\mathbf{E} + \mathbf{P} \ = \ \varepsilon_0 (1+\chi_e) \mathbf{E} \ = \ \varepsilon_r \varepsilon_0 \mathbf{E}.$

permeability is the degree of magnetization of a material that responds linearly to an applied magnetic field. Magnetic permeability is represented by the Greek letter

. The term was coined in September, 1885 by Oliver Heaviside.

In SI units, permeability is measured in Henry per metre, or newton per ampere squared. The constant value

? 0

is known as the magnetic constant or the permeability of vacuum, and has the exact or defined value

? 0

= 4?×10^?7 N·A^?2.

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