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 E in a conductor. The electric current density would then be j=ρv

where both charge density ρ and the velocity of charges v should be constant.


The movement is obviously created by a constant force acting upon the each charge q: F=qE


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.



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