1. A mechanical wave needs a medium for its propagation. An electromagnetic wave can travel through vacuum and it has the highest speed as it moves through the vacuum. Sound wave is a mechanical wave and light is an electromagnetic wave.
2. A mechanical wave can be both transverse and longitudinal but an electromagnetic wave is a transverse wave.
3. The particles of the medium vibrate, when a mechanical wave passes through it. In an electromagnetic wave the oscillating parameters are the electric and magnetic field. At any point on the line of propagation the field strength varies periodically with time.
4. Electromagnetic waves move much faster than mechanical waves. Speed of light in vacuum is 3 x l0 8 m/ s. Speed of sound in air is nearly 332 m/ s.
5. Mechanical wave is generated by the vibration of a particle in any material medium. Electromagnetic wave is generated by the accelerated motion of a charged particle.
6. Speed of an electromagnetic wave is inversely proportional to the refractive index of the medium. Speed of sound wave depends on the elastic properties of the medium.