Attaining speed of light with electric field

Click For Summary

Discussion Overview

The discussion revolves around the question of whether an electron can attain the speed of light when subjected to a very high electric field. Participants explore the implications of classical physics versus special relativity in this context.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant calculates the acceleration of an electron in a high electric field and finds a very short time to reach the speed of light, raising a question about the validity of this conclusion.
  • Another participant points out that while classical physics suggests rapid acceleration, special relativity modifies the relationship between force, mass, and acceleration, indicating that no massive object can reach the speed of light.
  • A third participant corrects the initial claim about acceleration, emphasizing that the correct formulation involves momentum and that speed approaches but never reaches the speed of light.
  • One participant acknowledges their lack of knowledge in special relativity, indicating a gap in understanding the implications of the discussion.

Areas of Agreement / Disagreement

Participants express differing views on the implications of classical physics versus special relativity, with no consensus reached on the initial claim regarding the electron's ability to reach the speed of light.

Contextual Notes

The discussion highlights limitations in understanding special relativity and the assumptions underlying classical physics, particularly regarding the behavior of massive particles in high fields.

zorro
Messages
1,378
Reaction score
0
I got this doubt while solving a problem.
Suppose an electron starts moving from rest in a region of very high electric field of the order or 106V/m along its direction.

Its acceleration is given by a=Eq/m, which is 1.758 x 1017m/s2 on substitution. We can ignore 'g' here.

The time taken to attain the speed of light is t = v-u/a = v/a = 1.71 x 10-9 s

How is it possible?
 
Physics news on Phys.org
Are you wondering why the time required is so short, or are you wondering why the electron achieves the speed of light at all when that is supposed to be impossible? The answer to the first question is that that is a tremendously large electric field and hence is produces a tremendously large acceleration that, in *classical* physics, would cause the electron to reach c very quickly. The answer to the second question is that in special relativity, a = F/m is not quite true, and is modified in such a way that no massive object can reach c.
 
Hi Abdul! :smile:

(try using the X2 icon just above the Reply box :wink:)
Abdul Quadeer said:
Its acceleration is given by a=Eq/m …

No, the correct formula is d/dt (momentum) = Eq …

so the https://www.physicsforums.com/library.php?do=view_item&itemid=53" can get infinitely large, but the speed stays less than c. :smile:

(for small speeds, of course, d/dt (momentum) is approximately ma)
 
Last edited by a moderator:
Ah, I still did not study special relativity. Thank you cepheid and tiny-tim.
 

Similar threads

Undergrad Electric field in a rotating frame
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad Work done by electric field of an irregularly shaped conductor
  • · Replies 3 ·
Replies
3
Views
2K
Undergrad Electric field of uniformly polarized cylinder
  • · Replies 5 ·
Replies
5
Views
3K
High School Direction of Electric Field & Field Due to a Dipole
  • · Replies 5 ·
Replies
5
Views
4K
Graduate Exploring the Electric Field of a Moving Charged Spherical Shell
  • · Replies 14 ·
Replies
14
Views
3K
Graduate Electron speed and acceleration in an electric field
  • · Replies 9 ·
Replies
9
Views
5K
Undergrad Electric field of a moving charge that's abruptly stopped
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Dimensional analysis in the formula for gyration frequency
  • · Replies 6 ·
Replies
6
Views
2K
Graduate Electric and magnetic field lines in a plane wave of finite extent
  • · Replies 1 ·
Replies
1
Views
2K
Graduate Horizontal component of the electric field of an infinite uniformly charged plane
  • · Replies 92 ·
4
Replies
92
Views
6K