Help with vector calculus in reflection and transmission of plane wave

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SUMMARY

The discussion focuses on the reflection and transmission of electromagnetic plane waves at a flat planar boundary between two media, utilizing vector calculus principles. The user seeks verification of their calculations involving electric fields, specifically the relationships between incident, reflected, and transmitted fields at the boundary defined by J.D. Jackson's equations. Key equations include boundary conditions for electric and magnetic fields, leading to conclusions about the relationships between the amplitudes of the waves and their angles of incidence and transmission.

PREREQUISITES
  • Understanding of vector calculus, particularly in the context of electromagnetic waves.
  • Familiarity with boundary conditions for electromagnetic fields as described in J.D. Jackson's "Classical Electrodynamics".
  • Knowledge of Snell's Law and its application to wave transmission and reflection.
  • Proficiency in manipulating vector equations and cross products in three-dimensional space.
NEXT STEPS
  • Study the boundary conditions for electromagnetic waves in J.D. Jackson's "Classical Electrodynamics", specifically equations (7.37a) to (7.37d).
  • Learn about the derivation and implications of Snell's Law in the context of wave optics.
  • Explore vector calculus applications in physics, focusing on cross products and their physical interpretations.
  • Investigate the mathematical representation of wave functions and their behavior in different media.
USEFUL FOR

Students and professionals in physics, particularly those specializing in electromagnetism, optics, and vector calculus. This discussion is beneficial for anyone involved in analyzing wave behavior at media boundaries.

yungman
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This is not a homework, this is concerning reflection and transmission of electromagnetic wave ( plane wave) at a flat planar boundary between two media. But the work in question is pure vector calculus. I ultimately want to proof if ##\vec E_I=\hat y E_I## then ## \vec E_R## and ##\vec E_T## are ##\hat y## direction also. I have a lot of difficulty in this as it is very long. I have the first road block that I need someone to check my work.

As shown in the figure, the ##\vec E_I,\;\vec E_R,\;\hbox { and }\;\vec E_T## are all in xz plane and the boundary is the xy plane at z=0.

At z=0, ##\vec E_I|_{z=0}=\vec E_{0I},\;\vec E_R|_{z=0}=\vec E_{0R},\;\hbox { and }\;\vec E_T|_{z=0}=\vec E_{0T}##

[PLAIN]http://i40.tinypic.com/kaj5x.jpg[/PLAIN]

We let:
##\vec E_{0I}=\hat y E_{0I}##.
##\vec E_{0R}=\hat x E_{0R_x}+\hat y E_{0R_y} + \hat z E_{0R_z}##
##\vec E_{0T}=\hat x E_{0T_x}+\hat y E_{0T_y} + \hat z E_{0T_z}##
##\hat k_I=\hat x\sin\theta_I+\hat z \cos\theta_I##, ##\hat k_R=\hat x\sin\theta_R-\hat z \cos\theta_R## and ##\hat k_T=\hat x\sin\theta_T+\hat z \cos\theta_T##.

This is the boundary equations of J D Jackson p304 (7.37) that is being used here
##[\epsilon(\vec E_0+\vec E_0'')-\epsilon'\vec E_0']\cdot \hat n=0## (7.37a) for normal E.
##[\hat k \times \vec E_0+\hat k''\times\vec E_0''-\hat k'\times\vec E_0']\cdot \hat n=0## (7.37b) for normal B.
##(\vec E_0+\vec E_0''-\vec E_0')\times\hat n=0## (7.37c) for tangential E.
##\left[\frac 1 {\mu}(\hat k \times \vec E_0+\hat k''\times\vec E_0'')-\frac 1 {\mu'}(\hat k'\times\vec E_0')\right]\times\hat n=0## (7.37d) for tangential B.
Where ##\hat k=\hat k_I,\;\hat k'=\hat k_T,\;\hat k''=\hat k_R##
##\vec E=\vec E_I,\;\vec E'=\vec E_T,\;\vec E''=\vec E_R,\;\hat n=\hat z##


(7.37a)##\Rightarrow\;[\epsilon_1(\vec E_{0I}+\vec E_{0R})-\epsilon_2\vec E_{0T}]\cdot \hat z=0## (A).
(7.37b)##\Rightarrow\;[\hat k_I \times \vec E_{0I}-\hat k_R \times\vec E_{0R}-\hat k_T \times\vec E_{0T}]\cdot \hat z=0## (B).
(7.37c)##\Rightarrow\;(\vec E_{0I}+\vec E_{0R}-\vec E_{0T})\times\hat z=0## (C).
(7.37d)##\Rightarrow\;\left[\frac 1 {\mu_1}(\hat k_I \times \vec E_{0I}-\hat k_R\times\vec E_{0R})-\frac 1 {\mu_2}(\hat k_T\times\vec E_{0T})\right]\times\hat z=0## (D).

From (C) ##[\vec E_{0I}+\vec E_{0R}-\vec E_{0T}]\times\hat z=0\;\Rightarrow\;\hat y E_{0I_y}\times \hat z + (\hat x E_{0R_x}+\hat y E_{0R_y} + \hat z E_{0R_z})\times \hat z + (\hat x E_{0T_x}+\hat y E_{0T_y} + \hat z E_{0T_z})\times \hat z=0##
##\Rightarrow\; \hat x E_{0I_y}-\hat y E_{0R_y}+\hat x E_{0R_y}+\hat y E_{0T_x}-\hat x E_{0T_y}=0##

Therefore ## E_{0I_y}+E_{0R_y}-E_{0T_y}=0\;\hbox { and }\;E_{0R_x}=E_{0T_x}## (E)


From (B) ##[\hat k_I \times \vec E_{0I}+\hat k_R \times\vec E_{0R}-\hat k_T \times\vec E_{0T}]\cdot \hat z=0##
Also according to Snell's Law, ##\theta_I=\theta_R##. Let ##\theta_1=\theta_I=\theta_R## and ## \theta_2=\theta_T## here.

\begin{align}\Rightarrow\; &[(\hat x \sin\theta_1+\hat z \cos\theta_1)\times \hat y E_{0I_y}+(\hat x \sin\theta_1-\hat z \cos\theta_1)\times(\hat x E_{0R_x}+\hat y E_{0R_y} + \hat z E_{0R_z})\\
&-(\hat x \sin\theta_2+\hat z \cos\theta_2)\times(\hat x E_{0T_x}+\hat y E_{0T_y} + \hat z E_{0T_z})]\cdot \hat z=0
\end{align} Because of the ##\cdot \hat z ## at the end, only the ##\hat x \times \hat y## terms in the equation remain:
##\Rightarrow\; E_{0I_y} \sin\theta_1 +E_{0R_y}\sin\theta_1 - E_{0T_y}\sin\theta_2=0##.(F)

If you compare (E) to (F)
It cannot be both true as ##\theta_1## is not equal to ##\theta_2##. Can anyone check my work, I have check 3 times already and I cannot see the problem.

Thanks
 
Last edited by a moderator:
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Anyone?

I have another question: The wave function is really defined as:
\vec E_R = \vec E_{0R} e^{-jk_R(x\sin\theta_1 - z\cos\theta_1)}=\hat k_R E_{0R} e^{-jk_R(x\sin\theta_1 - z\cos\theta_1)}
which the amplitude vary sinusoidally along the path of ##\vec k_R##. I should still use ##\vec E_R(\vec k_R)=\hat x E_{R_x}+\hat y E_{R_y}+\hat z E_{R_z}##. Is this true?
 
Last edited:

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