Electromagnetic waves are transverse and all travel at the same speed in a vacuum: 3 × 10⁸ m/s. In order of decreasing wavelength and increasing frequency, they are radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. They transfer energy from source to absorber, and higher frequency waves carry more energy.
Each type has uses. Radio waves carry TV and radio signals; microwaves are used for satellite communication and cooking; infrared for heaters, remote controls and thermal cameras; visible light for fibre-optic communication; ultraviolet for energy-efficient lamps and sun tanning; X-rays and gamma rays for medical imaging and treatment. Ultraviolet, X-rays and gamma rays are ionising: they can damage cells, causing skin ageing and cancer, and their dose is measured in sieverts.
Worked example
Why are X-rays useful for imaging bones?
- X-rays pass easily through soft tissue.
- Bone absorbs them strongly.
Answer:So bones show up as pale shadows on the image.
Key words
- electromagnetic spectrum
- the family of EM waves from radio to gamma
- ionising radiation
- can knock electrons from atoms, damaging cells
- infrared
- EM radiation given off by warm objects
- sievert
- unit of radiation dose
New questions every time.
NGSS-referenced: HS-PS4-4