Deriving Electric Field Energy Density

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SUMMARY

The energy density of an electric field in a vacuum is defined by the formula U = (1/2)ε₀E², where ε₀ is the permittivity of free space and E is the electric field strength. The derivation can be approached using Gauss's law, starting from the total energy expression of U = (1/2)∫(ρφ dV), where ρ represents the volume charge density and φ is the electric potential. The integral can be reformulated using the divergence of the electric field, leading to a clearer understanding of the relationship between electric fields and energy density. For a comprehensive derivation, consulting a physics textbook is recommended.

PREREQUISITES
  • Understanding of Gauss's Law
  • Familiarity with electric potential and charge density
  • Knowledge of integral calculus in physics
  • Basic concepts of electromagnetism
NEXT STEPS
  • Study the derivation of energy density in electromagnetic fields
  • Learn about Gauss's Law and its applications in electrostatics
  • Explore the relationship between electric fields and potential energy
  • Consult advanced electromagnetism textbooks for detailed explanations
USEFUL FOR

Students of physics, particularly those studying electromagnetism, as well as educators and anyone seeking to deepen their understanding of electric field energy density derivations.

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Homework Statement


I found on Wikipedia the formula for energy density of an electric field in a vacuum to be

U = \frac{1}{2}\epsilon_0 E^2.

I was wondering if someone could point me in the right direction to figure out how this was derived.


Homework Equations





The Attempt at a Solution


I was thinking maybe using Gauss's law?
 
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It starts with total energy = 1/2[Integral over volume(rho*phi*dV)], where rho is the volume charge density, phi the potential.

Then this has to be written as e0/2[Integral over volume(div E*phi*dV)]. After that you can break up the integrand into two parts.

You can try to do it from here, but it'd best if you look up a book.
 

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