Question

E cross H= Power

Curl(E cross H)=H (curl E)- E(Curl H)
H ( -dB/dt ) -E( J+ dD/dt)
for some reason they say J=0 , I don't get why?

Answer 1

@Preetha

Answer 2

J depends on what material is used.
In free space there are no electric charges,
and hence J equals to zero.

Answer 3

(same answer as Anonymous1921)
If you use this equation with reference to an electromagnetic wave travelling in a vacuum, there is not current there, so J = 0