Question

Question #edf8b

Answer 1

In electromagnetic theory, the Poynting vector describes the flow of energy per unit area in unit time in an electromagnetic field.

It may be defined as (in free space),

`vec S = 1/mu_0 (vec E X vec B)` where `vec E` and `vec B` are respectively the electric and magnetic fields.

It points in the direction of flow of energy.

It arises in the Poynting's theorem which expresses energy conservation in electromagnetic theory,

`(del(u_m + u_e))/(delt) + nabla*vec S = 0`

Where, `u_m` and `u_e` are respectively the mechanical and electromagnetic energy densities.

This is the analog of continuity equation in electromagnetic theory.