Which waves require a medium to propagate: light waves or sound waves?

• A. Sound waves require a medium; light waves can travel through a vacuum
• B. Light waves require a medium; sound waves travel in a vacuum
• C. Both require a medium
• D. Neither can travel in a vacuum

Answer: (A)

The main idea is that some waves need matter to move, while others can travel through empty space. Sound is a mechanical wave that propagates by vibrating particles in a medium such as air, water, or solids. Without a material medium, there’s nothing to transfer those vibrations, so sound cannot propagate in a vacuum. Light, on the other hand, is an electromagnetic wave. Its energy travels as oscillating electric and magnetic fields and does not require a medium, so it can propagate through empty space.

That’s why the statement that sound requires a medium while light can travel through a vacuum is correct. The other options misstate one or both parts: light does not require a medium, and sound cannot travel in a vacuum.