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(i) Define the term drift velocity. (ii) On the basis of electron drift derive an expression for resistivity of a conductor in terms of number density of free electrons and relaxation time. On what factors does resistivity of a conductor depend? (iii) Why alloys like constantan and maganin are used for making standard resistors? OR
Relaxation time is the time gap between two successive electron collisions in a conductor. The relationship between the relaxation time (𝛕) and drift velocity (V d) is given below. V d =-e (E 𝛕 m) Where. v d = drift velocity. e = charge of electron. E = field. m = mass of electron. 𝛕 = Relaxation time. 3. So the expression for ...
Similarly, the velocities of other electrons will be-. The average velocity vd of all the n electrons will be-. Here, The parameter V d is called drift velocity of electrons. The parameter T = (T 1 + T 2 + …. + T 3) / n = Average time between two successive collisions called as relaxation time. Now, let us define these terms-.
May 16, 2024 · 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 $ \tau$. Relation between drift velocity of the electrons (${ v }_{ d }$) and relaxation time (\tau) is given by, ${ v }_{ d } = -\dfrac { eE }{ m } \tau$ …(1) Where, E: Electric field
We now consider a very simple model of the collision integral, (∂f ∂t) † coll = − f − f0 τ = − δf τ . This model is known as the relaxation time approximation. Here, f0 = f0(r, p, t) is a distribution function which describes a local equilibrium at each position r and time t. The quantity τ is the relaxation time, which can in ...
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Relaxation time, drift speed, and current. A metal conductor with a square cross-section of side, l , carries a current, I = 3.6 A . The metal has 10 30 free electrons per m 3 drifting slowly at 10 − 5 m s . What is the length, l , of each side of the conductor?
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Drift velocity is the average velocity with which, the electrons drift in the opposite direction of the field. We start with the acceleration of the electrons, a = F/m = eE/m. The average velocity gained, i.e. the drift velocity, due to this acceleration = a*t = eEt/m. Here, t = relaxation time, the time between two successive collisions.
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- Mahesh Shenoy
