The electromagnetic spectrum

Electromagnetic waves are transverse waves that all travel at the speed of light in a vacuum. From long radio waves to tiny gamma rays, they make up the electromagnetic spectrum.

Key facts

  • Order (long wavelength to short): radio, microwave, infrared, visible, ultraviolet, X-ray, gamma.
  • Frequency and energy increase from radio to gamma.
  • All travel at 3 × 10⁸ m/s in a vacuum.
  • UV, X-rays and gamma are ionising and can damage cells.

Worked examples

Example 1

Put in order of increasing frequency: X-rays, radio, visible light, microwaves.

  1. Radio, micro, infrared, visible, UV, X-ray, gamma.
  2. So radio, microwaves, visible light, X-rays.

Answer: Radio, microwaves, visible light, X-rays

Example 2

A radio station broadcasts at 100 MHz. Find the wavelength.

  1. 3 × 10⁸ ÷ 1 × 10⁸ = 3 m

Answer: 3 m