Two fields at right angles

An electromagnetic wave is made of an electric field and a magnetic field, oscillating together.

The electric field and the magnetic field oscillate at right angles to each other. The wave travels in a direction at right angles to both of them.

Figure to be added

Figure 4.12 — an electromagnetic wave: the electric field oscillating in a vertical plane, the magnetic field in a horizontal plane, and the direction of travel along the line where they meet; one wavelength is marked.

Electric field

Oscillates in one plane.

Magnetic field

Oscillates at right angles to the electric field.

Direction of travel

At right angles to both fields.

Three directions, each at right angles to the other two: that is the whole geometry of an electromagnetic wave.