Radiation from accelerated charge

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Discussion Overview

The discussion centers on the phenomenon of electromagnetic radiation emitted by an accelerated charge, specifically exploring the source of energy associated with this radiation and the implications for calculations involving charged particles in electric fields. The scope includes theoretical considerations and implications for classical mechanics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants assert that an accelerating charge emits electromagnetic radiation, prompting questions about the source of energy for this radiation.
  • One participant suggests that the energy comes from the work done by an external force, which accelerates the charge and results in a loss of kinetic energy as radiation is emitted.
  • Another participant raises concerns about the applicability of classical mechanics in scenarios involving accelerating charges, particularly in relation to kinematic equations and energy loss.
  • It is proposed that the speed of a proton in an electric field cannot be accurately determined using standard kinematic equations without accounting for the energy lost to radiation.
  • Some participants indicate that the acceleration from the electric field is countered by a deceleration due to the loss of kinetic energy from radiation emission.

Areas of Agreement / Disagreement

Participants express differing views on the implications of radiation emission for calculations involving charged particles, with no consensus on the best approach to account for energy loss in classical mechanics.

Contextual Notes

Limitations include the assumption that classical mechanics can adequately describe the behavior of accelerating charges, as well as the dependence on definitions of energy loss and acceleration in the context of electromagnetic radiation.

azaharak
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If a charge undergoes acceleration it emits electromagnetic radiation.


Where does the energy associated with this radiation come from?


Thank you very much
 
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The charge recoils against the radiation and slows. Another way to look at it is that it is harder to accelerate a charged object than an equivalent neutral object.
 
azaharak said:
If a charge undergoes acceleration it emits electromagnetic radiation.

Where does the energy associated with this radiation come from?

Thank you very much

Whatever has accelerated the charge has put energy into it to get it going. An external force does work, the charge gains kinetic energy, then gives off some of this kinetic energy as radiative energy and slows down in the process.

Think of a circular particle accelerator speeding up small bunches of protons along its circular track. Energy from the electrical power grid is transferred into the electromagnetic control fields used to accelerate the protons. The protons then emit some of that energy as radiation.
 
So then in undergradaute texts, when your given a proton in an external electric field, and asked to find the speed of the proton after some time t, technically you can not use kinematic equations and assume the acceleration will be the field times charge divided by mass, as it should be loosing some of its kinetic energy simultaneously as it is accelerating.



Obviously we shouldn't even tackle this with classical mechanics.
 
well the accelerating will be that from the field, but its speed will be affected by some other deceleration which accounts for the lost kinetic energy too
 

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