Electromagnetic spectrum explorer – wavelength, frequency, photon energy, sources, uses and dangers
PhysicsOscillations & WavesAges 16–17
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Sign in to playDrag a cursor along the electromagnetic spectrum on a log scale, from radio waves to gamma rays, and read the wavelength λ, the frequency f = c/λ and the photon energy E = hf in joules and electronvolts. Each band lists sources, detectors, uses and dangers, says whether the radiation is ionising and whether it gets through the atmosphere to the ground. The Detectors screen shows the same room through the eye, a thermal camera, a microwave receiver, an X-ray image and a gamma camera.
Lesson: Electromagnetic waves: the EM spectrum, c = fλ, photon energy E = hf, ionising and non-ionising radiation, atmospheric windows
What it shows
All electromagnetic waves are transverse and travel through a vacuum at the same speed, c = 3.00 × 10⁸ m/s, so c = fλ links frequency and wavelength. Light is emitted and absorbed in photons of energy E = hf, so shorter wavelengths carry more energy per photon. The spectrum spans over 17 orders of magnitude, which is why it is drawn on a logarithmic scale. Photons above about 10 eV can ionise atoms, which makes X-rays and gamma rays harmful to cells. The atmosphere lets visible light and most radio waves through but absorbs most ultraviolet, X-rays and gamma rays.
How to use
Move the Wavelength (log scale) slider or drag on the spectrum; drag on the visible strip to set a colour precisely. Pick a source from Examples to jump to it. Read λ, f and E in the boxes below and the band card for sources, detectors, uses and dangers. Press Record to add rows and check that f·λ stays constant. Switch to the Detectors tab to see the same room through a different detector in each band.
Parameters you can change
- Screen Spectrum, Detectors
- Wavelength: log₁₀(λ / m) -13–4
- Show atmospheric transmission
- Show illustrative wave
Questions to explore
- How many times greater is the photon energy of a 50 keV X-ray than that of green light?
- Why can radio telescopes work on the ground while X-ray telescopes must be in orbit?
- Why can a thermal camera see a warm person but not the scene behind a glass window?
