Oscillating charge, larmor power dissipation

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Homework Help Overview

The discussion revolves around the behavior of a small charge in the presence of an incident electromagnetic wave, specifically focusing on the equations of motion, power dissipation, scattering cross section, and the conditions under which magnetic forces become significant. The subject area includes classical electromagnetism and oscillatory motion.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants discuss the equations of motion and power dissipation, with some expressing uncertainty about the correctness of their approaches, particularly in part (d). There is mention of dimensional analysis as a tool to verify results.

Discussion Status

Some participants have provided feedback on the attempts made, indicating that while certain parts are deemed acceptable, there are concerns regarding the accuracy of specific quantities used in the calculations. The discussion is ongoing, with no clear consensus reached yet.

Contextual Notes

Participants are navigating the complexities of the problem, including the need to replace certain quantities in their equations and the implications of their assumptions regarding the magnetic and electric displacements.

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Homework Statement



A z-polarized incident EM waves hits a small charge (-q) bounded to a massive charge (+q) with spring constant k0 and frequency ω.

(a) Write down the equation of motion

(b)Find time averaged total power dissipated.

(c) Find classical scattering cross section σ (thomson)

(d) Find value of E0 that makes magnetic forces non-negligible.

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The Attempt at a Solution



Part (a) and (b)
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Part(c)
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Part (d)
Because velocity of particle is slow, so magnetic force on it is low, giving it a small magnetic displacement compared to the electric displacement.

I related equated magnetic displacement to electric displacement to find a value of E0.

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I'm not sure if part (d) is right.
 
bumpp
 
bumpp
 
As far as I can tell:

(a) OK
(b) The mass occurring in the fraction part of your answer should be replace by some other quantity. Otherwise, OK.
(c) Fixing (b) will affect the answer for (c).
(d) OK

Note, you should make a dimensional analysis of your results. This would help you see that your answers for (b) and (c) can't be correct.
 
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TSny said:
As far as I can tell:

(a) OK
(b) The mass occurring in the fraction part of your answer should be replace by some other quantity. Otherwise, OK.
(c) Fixing (b) will affect the answer for (c).
(d) OK

Note, you should make a dimensional analysis of your results. This would help you see that your answers for (b) and (c) can't be correct.

I mistakenly thought p = momentum, but it should be p = qx, so the m2 should be replaced by charge, q2.
 
Right.
 

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