The difference between "electromagnetic field" and "electromagnetic wave"

ーーーーーーーーーーーーーーーーーーーーーーーーーーーーーーーーーーーーーーーーー

"Electromagnetic field" and "electromagnetic wave" are different concepts. We will explain the difference between them.

1. Electromagnetic Field (Electric and Magnetic Field)

An electromagnetic field refers to the space in which electric and magnetic influences exist. When an electric charge exists, an electric field (electric field) is generated around it, and when the charge moves, a magnetic field (magnetic field) is generated. The combination of this electric field and magnetic field is the electromagnetic field, and it has the following characteristics:

• Static and dynamic: Electric and magnetic fields can exist even when something is stationary - for example, an electric field exists in a non-current-carrying wire - and a magnetic field always exists around a magnet.
• Wide range of influence: Electromagnetic fields extend around charges and magnets, affecting other charges and magnets, especially those that are nearby.

2. Electromagnetic Wave

Electromagnetic waves are waves that travel through space with alternating electric and magnetic fields. Electromagnetic waves include light, radio waves, X-rays, and microwaves. Electromagnetic waves have the following characteristics:

• A time-varying field: Electromagnetic waves are transmitted in such a way that the electric field and magnetic field change over time in conjunction with each other, and they travel at right angles to each other. When the electric field changes, a magnetic field is generated, and this magnetic field further generates an electric field, causing the wave to propagate.
• Energy transport: Electromagnetic waves have the property of transporting energy. For example, energy is supplied to the Earth by the light (electromagnetic waves) that reaches the Earth from the Sun.
• Can travel in a vacuum: While electromagnetic fields are limited to a medium, electromagnetic waves can travel in a vacuum. This is how light and radio waves can reach outer space.

3. Summary of the main differences

• How they exist: The electromagnetic field is a concept that includes fields in which stationary objects (electrostatic fields and static magnetic fields) exist, while electromagnetic waves refer to the state in which dynamic fields are transmitted as waves.
• Whether they are transmitted: Electromagnetic fields tend to remain in place, while electromagnetic waves propagate through space to carry energy and information.
• The need for a medium: Electromagnetic fields are easily affected by media, but electromagnetic waves can propagate in a vacuum without a medium.


　Summary

An electromagnetic field is a field in which electricity and magnetism exist, and electromagnetic waves are a phenomenon in which that field fluctuates and travels through space as waves. Electromagnetic fields are static, associated with electric charges and magnets, while electromagnetic waves are dynamic, traveling through space while carrying energy.