Electromagnetic spectrum
The family of EM waves ordered by frequency: radio, microwaves, infrared, visible, ultraviolet, X-rays, gamma rays.
Last updated
Analogy
One piano keyboard, with visible light as a few keys.
Example
Radio: longest wavelengthVisible: 400 to 700 nmGamma: shortest
In practice
Visible light has wavelengths of about 400 nm (violet) to 700 nm (red).
Practice
Flashcards
- Which EM waves have the highest frequency?Gamma rays.
Questions people ask
What is the difference between radio waves and X-rays?
They are the same kind of wave with different frequency. Radio waves have long wavelengths and low energy, so they pass through bodies. X-rays have wavelengths around a nanometre or less, with enough photon energy to pass through soft tissue and ionise atoms.
How is photon energy related to frequency?
Each photon carries energy E = h f, where h is Planck's constant, 6.63e-34 J s. Higher frequency means more energy per photon. A violet photon at 7.5e14 Hz has about 5e-19 J, or around 3 eV, more than a red photon.