At a particular moment in time and space, we measure an electromagnetic wave's electric and magnetic fields. We find the electric field →E pointing Up and the magnetic field →B pointing North. What is the direction of wave propagation?

The direction of propagation is west.

Explanation:

We know that electromagnetic waves (EM-waves) are transverse in nature. EM-waves containing electric field and magnetic field both are perpendicular to the each other ( E ⊥ B ).

Transverse waves : the direction of propagation is perpendicular to the direction of amplitude which we call transverse waves. eg : light waves, water waves, gravitational waves etc.

Here, in our case the direction of electric field is pointing upward to the plan of the screen and the direction of magnetic field is pointing north

∴ ×

Where direction of electric field, direction of magnetic field, direction of propagation at particular instant.

Above equation follows right hand rule. put your finger toward you (out of the screen) then curl to the north side then  the thumb will give you the direction of the wave propagation ( west side )

In our case west direction is the direction of wave propagation.