Here's why:

* Electromagnetic waves are disturbances in electric and magnetic fields that travel through space. They do not require a medium to propagate and can travel through a vacuum.

* Mechanical waves require a medium (like air, water, or a solid) to travel. They are caused by the vibration of particles in the medium.

Examples of electromagnetic waves include:

* Light: Visible light is a form of electromagnetic radiation.

* X-rays: Used in medical imaging.

* Microwaves: Used in ovens.

* Radio waves: Used in communication.

Rays are often used to describe light rays, which are a simplified representation of how light travels in a straight line. Since light is an electromagnetic wave, rays are also electromagnetic waves.