All electromagnetic radiations travel at the same speed in vacuum.

All electromagnetic radiations travel at the same speed in vacuum.

• A. True
• B. False
• C. They travel at speeds that depend on frequency
• D. They travel slower than light

Answer: (A)

All electromagnetic radiation travels at the same speed in vacuum: the speed of light, c. This comes from Maxwell’s equations in empty space, which describe EM waves propagating with a universal speed that does not depend on frequency or wavelength. So photons of radio waves, visible light, X-rays, or gamma rays all move at c when there’s no medium around them. The reason some statements are not correct is that, in most materials, the speed of light depends on frequency due to dispersion—the refractive index varies with frequency—so different frequencies travel at different speeds inside a medium. However, in vacuum there is no medium to cause this; the speed remains constant for all electromagnetic radiation.

All electromagnetic radiation travels at the same speed in vacuum: the speed of light, c. This comes from Maxwell’s equations in empty space, which describe EM waves propagating with a universal speed that does not depend on frequency or wavelength. So photons of radio waves, visible light, X-rays, or gamma rays all move at c when there’s no medium around them.

The reason some statements are not correct is that, in most materials, the speed of light depends on frequency due to dispersion—the refractive index varies with frequency—so different frequencies travel at different speeds inside a medium. However, in vacuum there is no medium to cause this; the speed remains constant for all electromagnetic radiation.