How are electric and magnetic fields oriented in an electromagnetic wave?

In an electromagnetic wave propagating through ideal free space, the electric field and the magnetic field are oriented such that they are mutually perpendicular to each other and to the direction of wave propagation.12

These three vectors—the electric field, the magnetic field, and the direction of propagation—form a right-handed coordinate system. This relationship can be visualized using the right-hand rule: if you point your thumb in the direction of the electric field and your forefinger in the direction of the magnetic field, your middle finger will point in the direction of the wave's propagation.12

Because these fields oscillate at right angles to the direction of travel, electromagnetic waves are classified as transverse waves. While this transverse orientation is standard in a vacuum, the presence of boundaries or material media can alter this configuration, potentially introducing components parallel to the direction of propagation.12