All electromagnetic waves travel at the same speed in a vacuum.

• A. True
• B. False
• C. Only some travel at the same speed
• D. They travel at different speeds depending on frequency

Answer: (A)

In a vacuum, the speed of electromagnetic waves is a universal constant set by the properties of empty space itself. Maxwell’s equations lead to a propagation speed c = 1/√(μ0ε0), which applies to all frequencies. So radio waves, visible light, X-rays, and gamma rays all travel at the same speed in vacuum, about 3.00×10^8 m/s. The relationship v = fλ means frequency and wavelength trade off, so higher frequency waves have shorter wavelengths, but the speed remains the same. In other materials, speed can vary with frequency (dispersion), but in vacuum there is no dispersion and all frequencies share the same speed.