An excited hydrogen atom releases an electromagnetic wave to return to its normal state. You use your futuristic dual electric/magnetic field tester on the electromagnetic wave to find the directions of the electric field and magnetic field. Your device tells you that the electric field is pointing in the positive x direction and the magnetic field is pointing in the negative z direction. In which direction does the released electromagnetic wave travel? What convention can you use to describe the directions of the electric field and magnetic field, as well as the direction the wave travels?