Electromagnetic Waves and the Spectrum

Light, radio and X-rays as one family.

An electromagnetic wave is made of electric and magnetic fields oscillating at right angles to each other and to the direction of travel. Maxwell's equations predicted such waves, and they need no medium. In vacuum they all travel at about 3 × 10⁸ metres per second.

The family, from long to short wavelength, runs through radio, microwave, infrared, visible light, ultraviolet, X-rays and gamma rays. Only frequency and wavelength differ, and the product of the two is always the speed of light.

• Visible light is only a narrow band of the spectrum.
• Higher frequency means more energy per photon.
• Radio waves carry signals between antennas.

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