Question

What is a plane electromagnetic wave?

Answer 1

Waves are characterized by disturbances in the medium manifested in the form of vibrations. The waves travel at a specific speed and carry some amount of energy. These wave parameters help us define different types of waves.
Plane electromagnetic wave is a type of wave with distinct properties. It is based on the vibrations of the electric and magnetic fields.

Complete step by step answer:
Electromagnetic waves arise from the vibrations of electric and magnetic fields in the medium. A plane electromagnetic wave can be thought of arising from a plane surface acting as the source of an electric field.
Consider an infinite sheet of charge located in the y-z plane initially at rest with the surface charge density $\sigma$ . Now we know that an infinite sheet of charge would produce an electric field with the magnitude ${E_0}$ along the x direction. Now any disturbance in the electric field would simultaneously produce a magnetic field with the magnitude ${B_0}$ in the y direction. The fields are set up perpendicular to each other. The direction of wave propagation would be in the positive z direction.
Some characteristics of plane electromagnetic waves are:
Speed of the wave propagation: The electromagnetic waves travel at the speed of light.
Nature of the wave: The electromagnetic waves show transverse nature. This means that these waves do not require any medium to travel.
Nature of the fields: The fields associated with a plane electromagnetic wave are oscillating perpendicular to each other. Also, these fields are time varying.

Note:
The word plane does not mean that the electromagnetic wave is propagating in a single plane. Rather the shape of its wavefront gives it the name. This wavefront is planar because the respective directions of the electric and magnetic field decide the direction of wave propagation which is along an axis perpendicular to both.