What is an electromagnetic wave?

• A. Travels through a medium only
• B. Can move through a vacuum (empty space)
• C. Requires a material to propagate
• D. Is always transverse

Answer: (B)

Electromagnetic waves are disturbances that carry energy through space by changing electric and magnetic fields. They don’t need a material medium to travel; they can move through vacuum (empty space) at the speed of light. This ability to propagate in empty space is what sets them apart from many other waves that require a medium. They can also travel through air, water, or glass, but the key point is that vacuum propagation is possible. The other statements misstate this property: they are not limited to a medium, they don’t require material to propagate, and while they are typically transverse, the defining feature for this question is their ability to move through vacuum.