At a particular moment in time and space, we measure an electromagnetic wave's electric and magnetic fields. we find the electric field âe pointing north and the magnetic field âb pointing down. what is the direction of wave propagation?

Hi

perpendicular to magnetic field and electric field.

the magnetic field is always perpendicular to the magnetic field and direction of wave propagation is perpendicular to the both field.

these give us a right hand rule relating the direction .
1) keep your fingers in the direction of electric field.
2) curl your fingers toward magnetic field
3)the thumb of your hand show the direction of propagation .

hence

so direction of the wave propagation in 'west' direction .

thanks for asking

Biased means unfair but that's all ik