Poynting Theorem: Why is 1st Term Ignored?

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SUMMARY

The discussion centers on the application of the Poynting Theorem in calculating power, specifically addressing why the first term, representing the total energy stored in electromagnetic (EM) fields, is often ignored in certain scenarios. Participants clarify that the second term, which indicates energy flowing out of the EM fields, is primarily utilized in calculations involving current and Joule heating. It is established that the first term becomes significant when dealing with changing electric (E) or magnetic (B) fields, as its time derivative is non-zero in such cases. The third term, representing work done per unit time on charges, is also acknowledged, particularly in stationary states.

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  • Understanding of Poynting Theorem
  • Familiarity with electromagnetic fields
  • Knowledge of Joule heating principles
  • Concept of time-dependent vs. stationary states in electromagnetism
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  • Study the implications of time-dependent electric and magnetic fields in Poynting Theorem applications
  • Explore the derivation and significance of each term in the Poynting vector
  • Investigate Joule heating calculations in various circuit configurations
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Physicists, electrical engineers, and students studying electromagnetism who seek to deepen their understanding of energy flow and storage in electromagnetic fields.

quietrain
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why is it that when we use the poynting theorem to calculate power of

e.g, current flowing down a wire , which gives joule heating ,

we don't make use of the 1st term, but only the 2nd term is used?

910f60a9378cc62bee1e0bd603e62733.png


doesn't the first term give the total energy stored in the EM fields?

the 2nd term gives the energy flowing out of the EM fields

the 3rd term is the workdone per unit time on the charges right?
 
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If you look at stationary states only, i.e., if the fields are time independent, the first term vanishes. Otherwise it has to be included.
 
oh! so as long as i have E or B induction(changing) fields, i have to include the first term because its d/dt is not 0?

thanks!
 

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