Electromagnetic waves can travel without a medium.

• A. They require a medium to travel
• B. They travel only in air
• C. They travel faster than light in a vacuum
• D. They can travel without a medium

Answer: (D)

Electromagnetic waves propagate without a medium because changing electric and magnetic fields sustain each other. Maxwell’s equations describe how a varying electric field generates a magnetic field and a changing magnetic field regenerates the electric field, creating a self-propagating wave in empty space. In vacuum they travel at the speed of light, and in any material they slow down based on that material’s refractive index. This distinguishes them from mechanical waves like sound, which require a medium. The idea that they need air or that they travel faster than light in vacuum is incorrect. So they can travel without a medium.