Water waves and sound waves are examples of mechanical waves. Light waves are not considered mechanical waves. However, most of the mathematics and properties of mechanical waves applies to light waves. Basically, a mechanical wave is a disturbance which moves through a medium. Light waves are different from mechanical waves because they do not have to travel through anything. Light from the sun travels to the earth through space, and there is no air in space—it’s a vacuum. Light waves are just one type of wave called electromagnetic waves. All electromagnetic waves can travel through a vacuum. Other electromagnetic waves include the microwaves in your oven, radio and television waves, and X-rays.

Electromagnetic waves are created by the vibration of an electric charge. This vibration creates a wave which has both an electric and a magnetic component whereas mechanical waves usually correspond to variations in pressure or particle displacement of the medium in which they travel. In particular, light waves are regarded as a varying electric field (E) coupled with a varying magnetic field (B), at right angles to each other and to the direction of travel. This is depicted in the animation below.

An electromagnetic wave transports its energy through a vacuum at a speed of 3.00 x 10⁸ m/s (commonly known as "c"), i.e. the speed of light. The whole family of electromagnetic waves extends from gamma rays of very short wavelength (lower than 10^-10 m) to very long radio waves (greater than 10³ m). As for mechanical waves, light waves exhibit reflection, refraction, interference and diffraction and satisfy the relation   v = f λ.

THE PHYSICS OF WAVES