3
$\begingroup$

Let's consider the following tube (defined as the solid described by two arbitrary surfaces dA1 and dA2, and by all the rays which connect their boundaries):

enter image description here

I read in a textbook that, because of Poynting theorem, the flux of the Poynting vector through all the tube is necessarily 0 (and then this fact is used to prove that, since the flux through the lateral surface is 0, the flux through dA1 is the same of that through dA2). But I do not understand the first statement.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.