The magnetic field vec$(B)(z,t)$ of a plane monochromatic electromagnetic wave of wavelength $=663nm$ that is propagating in a vacuum in the $z$ direction is described by

vec$(B)(z,t)=B_{1}sin(kz-t)(hat(1{)}^2+j)$

where $B_1=11\mathrm{.}0{10}^{-6}T,$ and $1$ and J are the unit vectors in the positive$-x$ and positive$-y$ directions, respectively.