Which of the following is NOT an example of a mechanical wave?

• A. Light waves
• B. Ocean waves
• C. Seismic waves
• D. Sound waves

Answer: (A)

Mechanical waves need a material medium to transfer energy, with particles in the medium vibrating as the wave passes. Electromagnetic waves, like light, do not require a medium; they propagate as changing electric and magnetic fields and can travel through empty space. That’s why light waves are not mechanical.

The other examples involve a substance that must move or deform: ocean waves move water particles as the wave travels, seismic waves move through the earth’s materials, and sound waves rely on vibrating air (or other media) to carry the sound. So the one that is not a mechanical wave is light waves.