Slowing down a moving electric charge

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Discussion Overview

The discussion centers on the mechanics of slowing down a moving electric charge, specifically examining the roles of electrical and magnetic forces in this process. Participants explore the implications of force direction relative to displacement and velocity, and the conditions under which energy transfer occurs.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant asserts that an electric charge can only be slowed down by an electrical force, as magnetic force is perpendicular to displacement.
  • Another participant agrees but notes the absence of a referenced video, suggesting it may not be critical to the discussion.
  • A third participant reinforces the idea that while force is perpendicular to displacement, it is more relevant to consider force's relationship to velocity, stating that power is zero when force is perpendicular to velocity.
  • One participant argues that a magnetic force can change the velocity of an electric charge, specifically its direction.
  • Another participant counters that while the direction can change, slowing down implies reducing the magnitude of velocity, which cannot be achieved through a magnetic field.

Areas of Agreement / Disagreement

Participants express disagreement regarding the role of magnetic forces in slowing down an electric charge, with some asserting it is not possible while others suggest that magnetic forces can alter velocity direction.

Contextual Notes

Participants discuss the concept of force being perpendicular to displacement and velocity, highlighting the complexities of energy transfer and the implications of using infinitesimals in their reasoning.

Alex Schaller
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If an electric charge q is moving with a certain velocity v and we want to slow it down, this can only be done with an electrical force because magnetic force is perpendicular to displacement, correct? (watch video, time stamp 0:42)
video
 
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Yes. Although i see no video.
 
weirdoguy said:
Yes. Although i see no video.
It was only a pop video after all!
 
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Yes, I am thankful for whatever made it disappear.

Anyways, I wanted to write something in my first post, but I didn't, so I'll add it in this one, so that it's not completly useless:

Alex Schaller said:
force is perpendicular to displacement

This is true, but since this displacement is infinitesimal, I think that it is better to think in terms of velocity. Force is perpendicular to velocity at every instant, so it does not transfer energy, since it's power (scalar product of force and velocity) is zero. In general, keeping track of powers is easier than works done by forces.

I don't like infinitesimals.
 
The velocity of an electric charge is a vector quantity and it can be changed by a magnetic force.
 
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The direction can be changed. OP talked about slowing down, which means readucing magnitude of velocity, which can't be done by magnetic field.
 
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