Wednesday, February 6, 2019

electromagnetism - If we consider the electric field to act upon charges with a force, how does it stay in line with Newton's laws?


This should be a relatively simple question.


Let's say we have a constant electric field $\textbf{E}$ in a conductor. The electric current density would then be $$\textbf{j}=\rho \textbf{v}$$ where both charge density $\rho$ and the velocity of charges $\textbf{v}$ should be constant.


The movement is obviously created by a constant force acting upon the each charge $q$: $$\textbf{F}=q\textbf{E}$$


But constant force should give rise to acceleration and not constant movement. (Newton's Laws). Now I know there is an explanation here, that satisfies both ends, I was just unable to think of it.



Answer



Electrons does accelerate, increasing its drift speed until it collides with a positive ion of the metal lattice. It loses its drift speed after collision but starts to accelerate and again gains drift speed only to suffer a collision again and so on. On the average only, does the electron acquire drift speed and doesn't accelerate.



No comments:

Post a Comment

classical mechanics - Moment of a force about a given axis (Torque) - Scalar or vectorial?

I am studying Statics and saw that: The moment of a force about a given axis (or Torque) is defined by the equation: $M_X = (\vec r \times \...