The electromagnetic spectrum

Electromagnetic waves are transverse waves that transfer energy from the source to an absorber.
They form a continuous spectrum, and all types travel at the same speed through a vacuum or air: 3 × 10⁸ m/s.
In order of increasing frequency (decreasing wavelength): radio waves, microwaves, infrared, visible light (red to violet), ultraviolet, X-rays, gamma rays.
Our eyes only detect visible light, a very limited range of the spectrum.

How EM waves are made and absorbed

Different wavelengths are reflected, refracted, absorbed or transmitted differently by different substances and surfaces.
(Higher) Radio waves can be produced by oscillations in electrical circuits. When radio waves are absorbed, they can create an alternating current with the same frequency, which is how aerials work.
Changes in atoms and in their nuclei can generate or absorb EM waves. Gamma rays come from changes in the nucleus.

Radio waves: television and radio broadcasting. Microwaves: satellite communications and cooking food.
Infrared: electrical heaters, cooking food and infrared cameras. Visible light: fibre optic communications.
Ultraviolet: energy-efficient lamps and sun tanning. X-rays and gamma rays: medical imaging and treatments.
(Higher) Each use suits the wave's properties: for example, X-rays pass through soft tissue but are absorbed by bone.

Ultraviolet, X-rays and gamma rays can have hazardous effects on human body tissue. The effects depend on the type of radiation and the size of the dose (measured in sieverts).
Ultraviolet can make skin age prematurely and increase the risk of skin cancer.
X-rays and gamma rays are ionising radiation that can cause mutation of genes and cancer.

Use a Leslie cube: a hollow cube with four different surfaces (matt black, shiny black, matt white, shiny silver). Fill it with hot water.
Measure the infrared radiated from each surface with an infrared detector at the same distance.
Matt black surfaces are the best emitters (and absorbers) of infrared; shiny silver surfaces are the worst, and the best reflectors.

Electromagnetic spectrum: The continuous range of EM waves from radio waves to gamma rays.
Radio waves: EM waves with the longest wavelength, used for broadcasting.
Microwaves: EM waves used for satellite communication and cooking.
Infrared: EM radiation emitted by warm objects, used in heaters and thermal cameras.
Ultraviolet: EM radiation that can damage skin and cause skin cancer.
X-rays: Ionising EM waves used in medical imaging.
Gamma rays: The highest-frequency, ionising EM waves, from the nucleus.
Ionising radiation: Radiation that can remove electrons from atoms, damaging cells.
Leslie cube: A cube with differently finished faces used to compare infrared emission.