Drift Velocity From Field And Relaxation Time — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Drift Velocity From E And Tau This formula describes the steady-state average velocity of charge carriers (like electrons) in a conductor subjected to a constant external electric field, assuming frequent scattering events. Apply the force equation: F = eE, where e is the charge and E is the field. Relate force to momentum change over time: F = p t . In the relaxation model, the momentum change occurs over the relaxation time : p = m v = m v d, t = . Equating the force: eE = m v d . Solving for the drift velocity: v d = e E m . The electric field E must be uniform. The charge carrier mass m must be non-zero. The relaxation time must be positive. Confusing drift velocity (average steady motion) with the thermal velocity (random motion). Assuming the formula applies when the electric field is non-uniform or changing rapidly. Forgetting that the drift velocity is proportional to the relaxation time .