What is stress relaxation in polymers?
In materials science, stress relaxation is the observed decrease in stress in response to strain generated in the structure. Stress relaxation describes how polymers relieve stress under constant strain. Because they are viscoelastic, polymers behave in a nonlinear, non-Hookean fashion.
What is relaxation time in polymers?
Viscoelastic models of polymer behaviour incorporate a relaxation time which is defined as the ratio of the viscosity of the elements to their modulus (see the article on polymer models).
What is average relaxation time?
Relaxation time is defined as the time interval between two successive collisions of electrons in a conductor when current flows through it. It is denoted by τ. Relation between drift velocity of the electrons (vd) and relaxation time (\tau) is given by, vd=−eEmτ …( 1)
What is the value of relaxation time?
From a practical standpoint, this is what makes metals useful as electrical conductors even at room temperature, where a relaxation time on the order of 10-14 s and a mean free path (equal to the product of the velocity and the relaxation time) on the order of 10-8 m (or about 100 atomic distances) is typical.
What is T1 and T2 relaxation in MRI?
T1 (longitudinal relaxation time) is the time constant which determines the rate at which excited protons return to equilibrium. T2 (transverse relaxation time) is the time constant which determines the rate at which excited protons reach equilibrium or go out of phase with each other.
How does relaxation time vary with temperature?
When the temperature of the conductor increases, the resistivity of the conductor increases and hence according to the formula the relaxation period decreases.
What is meant by electron relaxation?
Define relaxation time of the free electrons drifting in a conductor: How is it related to the drift velocity of free electrons? Use this relation to deduce the expression for the electrical resistivity of the material. Answer: Relaxation time is the time gap between two successive electron collisions in a conductor.
What is meant by relaxation time of free electrons?
The average time elapsed between two successive collisions is known as the relaxation time of free electrons drifting in a conductor.
What is its relation with relaxation time?
It is the ease with which the electrons can travel in a conductor. So, the mobility of the electrons is directly proportional to the relaxation time of the electron.
What is SI unit of mobility?
The SI unit of velocity is m/s, and the SI unit of electric field is V/m. Therefore the SI unit of mobility is (m/s)/(V/m) = m2/(V⋅s).
What do you mean by mobility of charge?
Mobility of charge:- The mobility of a charge carrier is defined as the average velocity with which the free-electron move towards the positive end of a conductor under the influence of an external applied electric field.
What is mobility of a charge?
Electrical mobility is the ability of charged particles (such as electrons or protons) to move through a medium in response to an electric field that is pulling them.
Is mobility always positive?
But since electrical mobility is always positive, this means that the velocity is always parallel to the E-field regardless of charge. The values of mobility are given as positive for both electrons and holes.
Which type of charge carrier has the greatest mobility?
Which type of charge carrier has the greatest mobility? The mobility is proportional to the carrier relaxation time and inversely proportional to the carrier effective mass. The electron mobility is often greater than hole mobility because quite often the electron effective mass is smaller than hole effective mass.
Why does mobility decrease with temperature?
Mobility μ decreases with temperature because more carriers are present and these carriers are more energetic at higher temperatures. Each of these facts results in an increased number of collisions and μ decreases. That causes its drift velocity to be less than it would be at a lower temperature.
What is the effect of temperature on mobility?
At lower temperatures, carriers move more slowly, so there is more time for them to interact with charged impurities. As a result, as the temperature decreases, impurity scattering increases, and the mobility decreases. This is just the opposite of the effect of lattice scattering.
Why do Hall coefficients decrease with temperature?
The Hall Effectdescribes the behavior of free carriers in a semiconductor when electric and magnetic fields are applied. According to change in electric and magnetic field. As temperature increases at different magnetic field Hall coefficient decreases ,carrier concentration increases and Hall mobility decreases.
What is the effect of temperature on a pure n type and p type semiconductor?
In N type semiconductor, the number of free electrons (n) does not change appreciably with the increase in temperature, but number of holes (p) increases. In P type semiconductor, the number of free electrons (n) increases with the increase in temperature, but number of holes remains constant.
What is application of N-type and p-type semiconductor?
n-type and p-type semiconductors finds a great use in manufacturing electronic components. Diode is a combination of n-type and p-type semiconductors extensively used as a rectifier. Transistors are manufactured by keeping a layer of one type of semiconductor between two layers of another type of semiconductor.
Which is better’n-type or p-type?
Since the minority carriers are electrons and holes in p-type and n-type semiconductors, respectively, the order of increase in electron density in p-type semiconductor and hole density in n-type one are more sensible than increase in hole density in p-type semiconductor and electron density in n-type one, respectively …
How holes are created in n-type semiconductor?
Holes are formed when electrons in atoms move out of the valence band (the outermost shell of the atom that is completely filled with electrons) into the conduction band (the area in an atom where electrons can escape easily), which happens everywhere in a semiconductor.
What is p and n-type materials?
p-type and n-type materials are simply semiconductors, such as silicon (Si) or germanium (Ge), with atomic impurities; the type of impurity present determines the type of the semiconductor.