t+T
j = �c� ek

f
�c = �c t dt
+"

T
t





�c = � s �t - kx +� �! j = � s � �t - kx +� � ek

f



t+T �c = �� s j = �� s � ek
f



�c = �� s �t - kx +� dt = �� s
+"

T
t


t+T � t+T -kx+�


�t - kx + � dt = z dz =
+" +"
T � T
t �t-kx+�




� t+T -kx+�
dŚ = j dA � = j n dA = j dA

= - z dz =
[ ]
+"
� T
�t-kx+�
dA = dAn
z = �t - kx + � dz = � dt




Ś = j dA
+"

A


















"E "A "t
"E "A "t
c n
"E "A "t k
I = j = ek "t c n

j = ek "t c n ek =

"t
"A "t "A "t
n n
"A "t k
"An "An
n
"An





"E "A "t = �c "A � "t
c n n f





I = j = �c� ek = �c �
f f
j = �c � ek
f





I = � s � �
f


Drgania i fale 17 Drgania i fale 18