Question

can we say if at any instant for an electromagnetic wave if magnetic field is b then electric field is cb ? expalin. does that relation hold only for electric field amplitude and electric field amplitude

Answer 1

Electric field is cB when electric and magnetic field are perpendicular to each other.
The equation, E=cB hold for a plane wave in which the two electric and magnetic fields are perpendicular to each other . Hence, this quantity is proportional to the squared magnitude of electric field amplitude.
For a general electromagnetic field two electric and magnetic fields generally are not perpendicular to each other and so their magnitudes don’t hold in E = cB.