The speed of light
In a vacuum, every electromagnetic wave travels at the same speed: 2.998 × 108 m s-1.
In calculations this is used as 3 × 108 m s-1. In a material medium the speed is lower than in a vacuum, and the wavelength changes with it.
The speed of an electromagnetic wave
c = f λ
c = 3 × 108 m s-1 in a vacuum
This is v = f λ from the last skill, with the speed written c. Because c is fixed, a higher frequency always goes with a shorter wavelength.
Problem
A radio station broadcasts at a frequency of 1 × 108 Hz. What is the wavelength of its radio waves?
Solution
λ = c ÷ f
= 3 × 108 m s-1 ÷ 1 × 108 Hz
= 3 m