The electric field of a plane electromagnetic wave propagating along the x direction in vacuum is  E→=E0j^cosωt−kx. The magnetic field  B→, at the moment t = 0 is

Amplitude of magnetic field     B0=E0C  B0=E0μ0ε0E→×B→  is along direction of propagation∴j^×B^  must be parallel to i^     ∴B→ should be along k^  E→,B→  are in same phase∴B→=B0k^cosωt−kx B→=E0μ0ε0cosωt−kxk^  At  t = 0  B→=E0μ0ε0coskx  k^