Light momentum inside a dielectric medium?

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SUMMARY

When light enters a dielectric medium, such as glass, its momentum increases from \hbar k in a vacuum to \hbar\sqrt{\epsilon} k, where \epsilon represents the dielectric constant. This increase in momentum is reconciled with conservation laws, as the dielectric material itself acquires momentum during the interaction. The discussion clarifies that while the wavelength and wave velocity decrease by a factor of \sqrt{\epsilon}, the momentum is indeed altered due to the properties of the medium and the effects of reflection at the boundary.

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  • Understanding of light momentum and wave properties
  • Familiarity with dielectric materials and their constants
  • Knowledge of conservation laws in physics
  • Basic concepts of wave reflection and transmission
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  • Explore the properties of dielectric materials and their impact on light
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Physicists, optical engineers, and students studying electromagnetism or wave optics will benefit from this discussion, particularly those interested in the behavior of light in different media.

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Light in a vacuum has momentum \hbar k but when the light enters a dielectric medium, fx. glass, the momentum of the light is increased to \hbar\sqrt{\epsilon} k, where \epsilon is the dielectric constant of the dielectric. Where does the extra momentum come from? How can this be in accordance with conservation of momentum?

Thanks
 
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I would have argued (rather naively btw) that the momentum is hv/\lambda, and since the wavelength and wave velocity both decrease by a factor of \sqrt{\epsilon} that the momentum is not changed. How did you get that k increases by \sqrt{\epsilon}?
 
There is reflection at the boundary. Conservation of energy requires including the reflected wave. Conservation of momentum need not follow, because the dielectric material can acquire momentum.
 

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