Which of the following types of electromagnetic radiation travels the fastest?
a. radio waves
b. visible light
c. x rays
d. gamma rays
e. all of these travel at the same speed

E. All of these travel at the same speed

Explanation:

The speed of electromagnetic radiation does not depend on its frequency, but only on the properties of the medium.

For instance, in a vacuum all electromagnetic waves travel at the same speed, called 'speed of light', whose value is

and which is a fundamental constant.

When travelling in a medium, all electromagnetic waves slow down, according to the formula

where v is their speed in the medium, and n is called refractive index of the medium, whose value depends on the properties of the medium itself. As we see, there is no dependency on the frequency of the wave, so all electromagnetic waves travel at same speed.