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Physics 3 - Maxwell
Note from the Author
Table of Contents
What is this book
Historical facts
New aspects
Fully erroneous
Incorrectly interpreted

Physics 3 - Chapter 1
Equations
Complex vectors form
The Most General form
The General Solution

Physics 3 - Chapter 2
Solutions
Initial conditions
Non-homogeneous equation
Solution for three-directions
The four laws

Physics 3 - Supplement
Fermat's proof
Beal's conjecture
Pythagorean triples
Inertial mass
Gravity constans big G
What does the Moon look at?

Physics 3 - Final notes
Final notes

Physics 4 - New book
Entry

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2.3.  Solutions for three-directional equation

2.3.1.  Solution for three-directional homogenous equation

     For three dimensions, instead of 2w76a we apply 2w76b ,
2w76. (2.76)
     Perhaps nabla (del) operator squared also called Laplacian, unjustifiably scared some people interested in solution of Maxwell’s equations.
     We can find in related publications various attempts to solve these equations, mainly based on simplifications or on imposing additional conditions.
     Paul Dirac asked his coworker “Is your thinking algebraic or geometrical?”. Richard Feynman similarly treated comprehension – he stated that to understand a problem means when looking at equation, one cannot see its algebraic transformations but its solution.
     Let’s then look “geometrically” at equation (2.76). Without sacrificing details,
we can skip vector sign over  F and analyze this form:
2w77. (2.77)
Equation (2.77) describes the behavior of function 2w77a in point 2w77b without any sources at this point, which is depicted on Fig.3.
x z Sorry, your browser does not support inline SVG.
Y
r
F3
F2
F1
/div>
Fig.3    
Notations on the drawing
x, y, z – coordinate system
r - position vector for analyzed point
F1, F2, F3 – example of waves (denoted by double arrow)
                     solid line denoted waves passing through the point,
                     broken line denotes fragments of the same waves which are
                     not passing through the point

      Homogenous wave equation (2.77) contains all possible waves passing through
point 2w77b, generated in points where equation (2.1) includes wave sources.
      Both parts of equation (2.77) contain in themselves a sum of possible waves while the quantity of these waves in general case is determined by quantity of sources which can be continuously distributed in space.
      Since this is a linear differential equation, this equation must be satisfied by sum of all waves as well as by each of individual waves. This allows us to deal only with single wave (i.e. single solution) which passes through any given point at any selected one-direction e.g. assuming that wave source is at this direction).

Direction can be expressed as:
wˆ = wx∙ xˆ + wy∙ yˆ + wz∙ zˆ  ,
where
wˆ , xˆ , yˆ , zˆ    – unit vectors
wx ,wy ,wz  – unit vectorcomponents, wˆ  ,
                     which satisfy relation: wx2 + wy2 + wz2 = 1  .
      Denoting the position of analyzed point by  r0   , for pencil of lines passing through this point we can then express all position vectors as   r  = r 0 + ξ  ∙ wˆ    and corresponding value of the function as
2w78. (2.78)
      For defined   r0     and  wˆ  we will use short form  F(r   , τ ) = Fξ ( ξ , τ ) remembering that function   Fξ ( ξ , τ ) is determined for specifically defined parameters    r0     and  wˆ  .
      We will introduce one more variable  R  and its vector equivalent variable  R   = wˆ  ∙  R , which will be used in further formulas.
Using new notations, we have
2w79a,
2w79b,
2w79c.
So, we can see that
2w79 (2.79)
      Thus, our three-directional equation became one-directional equation, already
well worked out:
2w80 (2.80)
for which we can determine solutions.
      When we can see that a solution is independent of other dimensions, we usually assume that this one-directional solution is represented by planewave.
      The solution of an equation in the form of  Fξ ( ξ , τ ), exhibits several similar features, but it cannot be considered as a planewave since it only determines course of a function on straight line  ξ ∙  wˆ    passing through the point  r 0  .  In order to obtain value of the function in point   r 0 , we must sum up all solutions at all directions   wˆ    passing through point   r 0 . If we denote elementary spherical angle as , then using radian measure of angle
we obtain
2w81 (2.81)
Subscript index  p  in the notation of function   Fp ( wˆ  ∙ ξ , τ ) represents incoming wave from direction  wˆ ,   thus we need to consider influence of direction in determining function Fp ( wˆ  ∙ ξ , τ ).
      For Maxwell’s equations the value of  Fp ( wˆ  ∙ ξ , τ )  represents vector and integral equation is expressed in following form:
2w82 (2.82)

2.3.2.  Solution for nonhomogeneous equation

      The relations (2.80) and (2.82) allow us for deriving the solution of nonhomogeneous equation for three directions.
     Complementing equation (2.80) with forcing functions  f ( r  , τ ) which appear in (2.1) and which act only in chosen direction, i.e.   fw, ξ ( wˆ  ∙ ξ , τ ) we obtain the equation:
2w83 (2.83)
for which similarly to (2.74) and (2.75) we can formulate following solutions:
2w84 (2.84)
2w85 (2.85)
To indicate that functions  f ( r  , τ ) ,  Fv  and  Fu  are related only to chosen direction, we assign to them subscript  w . The same applies to function  Fo 
from formula (2.69) therefore, we obtain:
 Fow ( u0 , v0 ) =  Fvw ( u0 , v0 ) +  Fuw ( u0 , v0 ) (2.86)
Inner integrals in equations (2.84) and (2.85) depend only on R.
Denoting  Fow, R () as their indefinite integrals:
2w87 (2.87)
equations (2.84) and (2.85) can be written as
2w88 (2.88)
2w89 (2.89)
and after applying (2.86) we have:
2w90 (2.90)
 Fow ( u0 , v0 ) in equation (2.90) corresponds to  Fp ( r 0 +  wˆ  ∙  ( ξ = 0 ) , τ)  
in equation (2.81).
It can be noted that
2w90a and 2w90b
represent waves coming from opposite directions.
     Also, integral of waves incoming from all directions is a sum of integrals on the same hemisphere
2w90c for first hemisphere
2w90d or second hemisphere.
     Reversal of directions, thus change of  w  to  -w  is equivalent to change of integration sign. The sum of both of these integrals can be obtained by integrating on whole sphere using one of the formulas below:
2w91 (2.91)
or
2w92 (2.92)
Value  F ( r0  , τ ) represents a vector, so correct equations are:
2w93 (2.93)
or
2w94 (2.94)



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